I bought a iPhone 7 256GB, primarily because Verizon is offering $650 for my 6 in the form of bill credits over 24 months.
I'm debating returning the 7 for the reasons below.
Screen
This is by far my biggest and number one reason. I went through a major struggle on my 6 to get a screen free of defects (more details here). I was happy to see that my iPhone 7 has ZERO dead pixels, but it has three issues:
1) I can see the digitizer. There are faint diagonal lines across the entire screen I can see in dark environments on white and light colors. I can see these lines every night while laying in bed and using the phone (more details here).
2) Yellow screen, the white point is warmer than my 6 and its more yellow than I'd like. I admit I prefer a cool "snow" white, but if I saw snow the color of the whites on my 7...I wouldn't eat it.
3) My 6 screen is brighter. Apple claims a higher brightness on the 7 screen. Mine is dimmer, in addition to being yellower.
Bluetooth
Ever since switching, my phone Bluetooth headset will say 'disconnected' immediately followed by 'connected'. This is annoying and didn't happen once on my 6 (more details here).
Speaker
I immediately noticed the stereo speakers on the 7 and like it quite a bit. But the speaker on the bottom is not as loud as the 6. (The front facing speaker doesn't make up for this as the bottom speaker on the 7 is louder than the front facing speaker, so stereo imaging actually works), if I'm listening to a podcast from the other side of the room, I can hear it better on my 6. A minor quibble and NOT a reason I'd return it, I just thought I'd mention it.
UI
I'm not sure if Apple is on a warpath to playschool or what but they've lost their way since iOS 6. I've got 8.3 on my 6 and I notice most of the UI elements in iOS 10 are simply ginormous by comparison. Most of the changes do not make the UI better. Also, the micro stutter on the app close animation is annoying. So is the keypad brightness glitch (if you have a 7, open the phone app, tap keypad, press home and tap the phone app icon again. It does a weird screen brightness adjustment that doesn't exist even on iOS 10 on previous iPhones). My 6 has tons of stutter and problems, but the 7 benchmarks over 2X faster...I expect more. I've grown used to these iOS 10 changes and I wouldn't return it because of it alone, but it adds to the frustration.
2-year Commitment
I went through devices like water before settling on the iPhone 5 with jailbroken iOS 6.1.2. That was the best combination I've ever used. If I knew then what I know now, I never would have updated to iOS 7.
I only have the 7 because Verizon is doling out $650 for my 6. Unfortunately its in the form of 24 credits that will stop if I swap the phone for another. I have to decide NOW if I will keep the phone for a full 24 months to receive the full $650. If I end up wanting an iPhone 8 or whatever is released in 12 months, I'll only get $325 credit value for my 6.
Final thoughts
I think I'm going to exchange it and see if the exchange is better (primarily that screen issue). IF it is, I'll keep it, if not...back to the 6.
¯\_(ツ)_/¯

I'm debating returning the 7 for the reasons below.
Screen
This is by far my biggest and number one reason. I went through a major struggle on my 6 to get a screen free of defects (more details here). I was happy to see that my iPhone 7 has ZERO dead pixels, but it has three issues:
1) I can see the digitizer. There are faint diagonal lines across the entire screen I can see in dark environments on white and light colors. I can see these lines every night while laying in bed and using the phone (more details here).
2) Yellow screen, the white point is warmer than my 6 and its more yellow than I'd like. I admit I prefer a cool "snow" white, but if I saw snow the color of the whites on my 7...I wouldn't eat it.
3) My 6 screen is brighter. Apple claims a higher brightness on the 7 screen. Mine is dimmer, in addition to being yellower.
Bluetooth
Ever since switching, my phone Bluetooth headset will say 'disconnected' immediately followed by 'connected'. This is annoying and didn't happen once on my 6 (more details here).
Speaker
I immediately noticed the stereo speakers on the 7 and like it quite a bit. But the speaker on the bottom is not as loud as the 6. (The front facing speaker doesn't make up for this as the bottom speaker on the 7 is louder than the front facing speaker, so stereo imaging actually works), if I'm listening to a podcast from the other side of the room, I can hear it better on my 6. A minor quibble and NOT a reason I'd return it, I just thought I'd mention it.
UI
I'm not sure if Apple is on a warpath to playschool or what but they've lost their way since iOS 6. I've got 8.3 on my 6 and I notice most of the UI elements in iOS 10 are simply ginormous by comparison. Most of the changes do not make the UI better. Also, the micro stutter on the app close animation is annoying. So is the keypad brightness glitch (if you have a 7, open the phone app, tap keypad, press home and tap the phone app icon again. It does a weird screen brightness adjustment that doesn't exist even on iOS 10 on previous iPhones). My 6 has tons of stutter and problems, but the 7 benchmarks over 2X faster...I expect more. I've grown used to these iOS 10 changes and I wouldn't return it because of it alone, but it adds to the frustration.
2-year Commitment
I went through devices like water before settling on the iPhone 5 with jailbroken iOS 6.1.2. That was the best combination I've ever used. If I knew then what I know now, I never would have updated to iOS 7.
I only have the 7 because Verizon is doling out $650 for my 6. Unfortunately its in the form of 24 credits that will stop if I swap the phone for another. I have to decide NOW if I will keep the phone for a full 24 months to receive the full $650. If I end up wanting an iPhone 8 or whatever is released in 12 months, I'll only get $325 credit value for my 6.
Final thoughts
I think I'm going to exchange it and see if the exchange is better (primarily that screen issue). IF it is, I'll keep it, if not...back to the 6.
¯\_(ツ)_/¯