Coming from an iPhone 11, obviously the differences are huge and the upgrade is 100% worth it.
Initially, I proceeded with the purchase 1 month before the release of the 17 and the reason is clearly for my aesthetic; visually, the Pro models of the 17 series did not appeal to me at all even though, of course, they are more powerful devices. Small disclaimer: the base model of the 17 series now has many features of the Pro models (120hz screen etc.) and it makes sense since you are paying almost a thousand euros for a phone. This should have happened a long time ago…
As for the phone now, I use it for daily use and of course you have all the basic privileges that every iPhone user out there has. Multitasking is top-notch and the phone runs super smoothly, it doesn't struggle anywhere. For gaming, I wouldn't recommend it clearly because of its size; the wiser choice is the Pro Max, which also comes with the price tag. The battery is excellent—ideally, try to keep it between 20%-80% and it will last you forever (my iPhone 11 currently has 82% battery health after 4 and a half years of daily use only because I took care of its charging. It's more important than we think). I don't think I need to mention photo and video quality; after all, it's one of the biggest selling points of the Pro models every year. So far, I have nothing negative to report, which makes sense after only a month of use.
A useless feature of the device is the camera button they added on the right side below the power button. Clearly a marketing move and it's just a way to visually distinguish the 15 from the 16 when talking about Pro models, at least that's how I see it.
Overall, if you're not a brand enthusiast like me or don't intend to take full advantage of the phone's capabilities, I definitely don't recommend going for this phone, and that's clearly because of its price.
Personally, however, so far I am completely satisfied and there will be another update in the future.

Coming from the 13 mini, I finally made the decision to change my phone, or rather to upgrade, and I went for the pro series. The phone is flawless, exactly what I expected.
But let's break it down:

Battery: truly flawless, almost perfect. I have set the phone not to charge above 80% to keep the battery health above 90% for as long as possible. As many YouTubers have said, the 16 series has a lithium battery, and if the phone stays plugged in for many hours, it degrades much faster. In short, it easily lasts me a whole day, even with stress tests in games and several hours on social media.

Cameras: I have not the slightest complaint. With the right settings, photos come out unbelievably good. I don't care about having the best zoom resolution; it seems insignificant to me. 5x optical zoom in photos is more than enough for the average user.
As for video, ProRes is the best I've seen on a mobile device. It requires a lot of space, but it gives you the opportunity to edit the video as you wish. I'm not experienced, but from other videographers I know, they are speechless—it's like having a small mirrorless camera in your pocket. That's the summary.

Processor: very powerful, indeed it doesn't lag anywhere. Personally, I do a lot of stress tests and have seen it run even at 1fps. I wouldn't say it's unexpected; I think it's logical. In any other use of the iPhone, it doesn't lag at all—flawless! No exaggeration.

RAM: more than enough, it hasn't caused me a single problem.

Screen: convenient for one hand, crystal clear, very bright during the day, beautiful colors—after all, we're talking about OLED.

Back: matte finish, doesn't leave fingerprints, or if it does, it's minimal. Titanium all around, beautiful, sturdy, and light. It cleans very easily with a glasses cloth.

I have only one complaint, and I believe many others who pay 1000+€ for a premium device have it too: it doesn't start at 256GB as we saw in the 17-17pro series and so on.

I've owned it for 1 month, these are general observations.
I will return with more.

I upgraded from iPhone 11 Pro. The difference is vast. I placed them side by side to see the difference between 60Hz and 120Hz screens; the difference is noticeable, but even if it didn't have it, it wouldn't bother me at all (companies create needs for us that we essentially don't have). The camera works wonders, and I haven't even tested it in demanding situations yet. The battery lasts a day comfortably, but it's the classic Apple battery that sooner or later will need charging twice a day, which is ridiculous for the phone's price (it should have at least 4000mAh for such a price). In the unnecessary features, I would add the action button (I already miss the old good silent button) and the zoom on the right side of the phone; apparently, Apple is trying to add unnecessary things to inflate prices. Not to mention that because of this, a part of the side remains exposed in protective cases, making it very easy to get scratched even with a case! Another thing that I personally didn't like so much, maybe because I have to get used to it, is the size. I'm a fan of more compact phones and loved the small and ideal size of the 11 Pro. Other than that, it's a premium device that is NOT worth getting if you're satisfied with just a very good camera and don't want a professional one. Get the 16; the only difference is in Hz and the camera (and it's smaller in size). Finally, I should mention that I think it's worth the upgrade if you have a device from iPhone 12 and below. If you have an Android, don't think too much about it; no Android will accompany you like a soldier for 5+ years tirelessly like these

Coming from the iPhone 14 Pro, I can't say that in typical use I noticed differences basically, I didn't notice any. However, I did see some upgrades in the operating system, some of which could have been implemented on the 14 Pro as well. The design remains just as beautiful as before. Beyond that, regarding the two new buttons, I miss the old silent button a bit, but okay, I've gotten used to it and it doesn't bother me as much as I expected.

Now, regarding the new camera button, which has been talked about a lot, it is fully functional, it doesn't lag, it doesn't freeze, as some say, and personally I enjoy it and it has been convenient for me. I say this because some criticize it, others find it indifferent, but okay, everyone has their opinion. In general, be cautious with reviews. Many criticize just for views, because it sells more to bash Apple. I saw videos and reviews that, honestly, were not accurate.

As for whether it's worth it for someone with the 14 Pro to upgrade to the 16 Pro, for me it’s only worth it if they intend to take advantage of the improvements in video capabilities. Many more features + SSD recording with Type-C. With the 14 Pro 256GB, I had serious space issues. One of the reasons I switched to the 16 Pro was that I can now write to external drives. Another reason was the 4K 120fps, but here you need to be careful about what drive and cable you get. If you don't get a fast drive and cable, it won't work.

Be careful with storage. I had the 14 Pro 256GB and everything was fine. However, a friend of mine had the 128GB and couldn't shoot 4K ProRes due to space. I don't know if this applies to the iPhone 16 Pro as well, I didn't look into it, I just got the 256GB to be sure.

Finally, I would like to thank the Skroutz team. When I placed the order, I didn't notice it, but the system had selected a store from France, and the phone would take over 10 days to arrive. I contacted Skroutz, and the people were very helpful and professional. I asked them if it was possible to change the store, and not only was it changed, but Skroutz covered the price difference, as the other store had the phone 48 euros more expensive.

Coming from the 15 Pro Max, I have to say the following. Finally, what I was waiting for has happened, and that is the small increase in inches in the Pro models where they have finally raised it from 6.1 inches to 6.3 inches, making it the ideal size in terms of practicality.
So let's get to the point.
Differences compared to the 15 Pro Max:

Battery: I believe it is the same as the 15 Pro Max in terms of usage duration, regardless of the fact that the numbers are lower. (This is probably due to better energy management that the A18 Pro will provide.)

Face ID: I have to say that where the 15 Pro Max struggled was in complete darkness, and here comes the 16 Pro that really doesn't falter anywhere, and the Face ID works literally everywhere and instantaneously.

Camera:
The wide-angle is finally clearer.
The zoom has become much clearer and more stable (in video).
Also, finally, the night shots look like it's evening outside, meaning you can now take brighter photos.
The addition of the side camera button is a pleasant addition in my opinion. Also, in zooming and unzooming, it becomes more precise how much you want to zoom with the button, as well as giving you other functions in the camera (f, effects, tones, etc.), so it's a positive addition.

Overall, in terms of performance, I believe it is a small click better than the already excellent 15 Pro Max.

Also, one detail that I must emphasize is that with the 15 Pro Max, I had noticed that the device would sometimes heat up noticeably, which I have not observed so far with the 16 Pro, and if it has happened, it was certainly to a much lesser degree.
And the best part is that later it will be able to accept (Apple Intelligence), which will do magic for those who know.

One thing bothers me, as it did with the 15 Pro Max, and that is that I would like an even better battery.
Come on, put a battery in it that will finally last us comfortably for a day.
(Those of us who use social media, apps, and have 5G and Bluetooth constantly on know that it doesn't satisfy us as much as we would like).

In conclusion, we are talking about a flawless phone-tool-multitasker that does everything and does it e-x-c-e-l-l-e-n-t-l-y.

Sheet.
I have never had an iPhone until now.
My recent devices were Honor 20 Pro, S20 FE, 1+10, S23U, and I decided to switch camps after a friend's suggestion since I was tired of some things that I won't analyze now. (As if I would even sit down to do that, hehe)
For the record, I was between this and the Xperia 1 VI. (During Black Friday, it was 1100, 150 less than this, which I saw up close and it was indeed impressive too)
I try to avoid Xiaomi-type phones with all the sympathy I have for those who like them; I would never spend 1200+ euros to buy such devices, and don't let some random, biased YouTubers lead you into bad purchases.
Benchmarks don't always tell the truth, and the dry numbers are just a snapshot that should concern the average user very little.
When you spend that kind of money, you have expectations, and this (and the corresponding Samsung Ultra) meets them.
Let's get to the point. In this size, you have three options: this, the S24, and the Pixel, as unfortunately, the other worthy device (Vivo X200 Mini) won't come.
Super positives. VIDEO. There is no comparison, guys. Huge size, especially at 4K 120fps, it's insane.
Positives. Photos (macro, zoom, night all super, I like that it captures what you see, it doesn't make them more vibrant at first glance), screen, speed, small size without overheating, at the end of the day with my personal use it stays at 35-45%.
Sound quality is top-notch, connectivity is amazing (and the S23U was amazing too; these are the things you pay for and don't see).
Selfies seem somewhat better than those of the S23U, but since I hardly use it, I have no opinion.
Negatives. Charging. It could charge a bit faster, but okay.
What I miss from Android are the mod apps and that's it.
Now those who sit there tell you that it's not a customizable device, etc., if you want to turn your device into a circus and that you will put Santa Claus icons and have a ringtone of bugs, that's a buying criterion, get something else.
Here you have the basics, which you didn't have before according to what older users say, which for me is more than enough.
The closed ecosystem is another negative, which personally doesn't bother me for now; I plan to get a MacBook at some point.
Also, I have set the button on the left to mute when I press it; you can set various things, and I initially felt the camera button was a bit unnecessary, but now I only open the camera from there. It's fun.
The black color is amazing and reminds me of Batman vibes.
Jokes aside, it's a lightweight small device that is worth considering if you plan to spend a boatload of money on it, which is quality and will have value after two to three years if you want to change it.
If you can get the 256, get that; it's unfortunate that it has 128 as the base, but okay, if you max out at 128, get this like I did, and I'll have an SSD to transfer files every so often. (For video 01:55 seconds, 4K 60fps Dolby Vision HEVC - 807.9MB. For photos, 24MP HEIF on the main camera 2.9MB, while at 12MP 1.3MB)
EDIT 1. I must mention Face ID. We're talking about lightning speed. Nothing compares to all the others. I was really wondering how the fingerprint could be replaced, which I find terrible, especially those on the screens. The simple old ones that were on the side are clearly superior and more reliable.
FACE ID is from another planet.
Edit 2. In my initial charges, after an overnight charge, the next morning it wouldn't turn on at all and my heart sank. It's a common little issue that exists. Solution: volume up, volume down, and the power button until it turns on and you see the logo. (It's unacceptable, but okay, shit happens.)
Edit3. Today I recorded a video in a somewhat noisy closed space with speeches, etc. It has a setting that you can tweak even after recording, in the style of audio profiles for videos. This works wonders. It eliminates most of the annoying sounds and focuses on the speeches. Impressive clarity overall, nice tricks with the sounds. Owners, give it a try.
Edit4. For the transfer speeds of 3.2 gen2, you need to buy a different cable to achieve them. (And make sure to plug it into the correct port on the PC :-))
If I have any issues, I will follow up.