1 full day in on the smaller s8. Coming from a Nexus 6p.
Touchwiz - couldn't stand a variety of things about it, and within 30 minutes I installed Nova again. Maybe I'm just getting too old (47) and set in my ways, but I ended up setting up everything just like my 6p. A deal breaker on touchwiz for me was the dumb decision for swiping up *and* down on the screen to open up your app drawer. With how tall these phones are (how are you s8+ people dealing with this??) Nova is a fantastic solution for one-hand swiping down of the notifications from anywhere on the screen.
Side gripe: a bunch of app makers need to start redesigning apps for nav buttons to be at the bottom of the screen, where you can actually reach it with your thumb. I read someone else coming from an iphone complaining how the Android Twitter app is dumb because of this (iphone Twitter app nav buttons are at the bottom). This is why I am actually trying the Samsung stock browser instead of Opera or Chrome. Jury is still out.
Battery - seems good so far. I have the AOD display on, with one of the cool little background patterns you can select. I left the phone unplugged last night at 100% and 10-ish hours later came down to 89%. Doesn't seem to drain horribly quickly with normal usage, but still need a few days to see.
Lag - seems minimal so far. I noticed Twitter, LinkedIn and FB can be a little choppy when scrolling down the first time, at full speed, but how often do you do that? You are usually scrolling somewhat slowly to scan for stuff to read. I did activate developer options and reduce the 3 animation scale options to 0.5x so it makes transitions between apps and home screens very snappy. Time will tell on whether or not lag gets worse.
Size - I think the s8 is perfect and think the s8+ would have been too big for me, and I am 6'3" with appropriate hands for my height (wear size L gloves). But then again I thought the 6p was too big. You still can't one-hand the phone, but I know this will fit in my pockets easier than the + would have since the + is a tad taller than the 6p. My finger hits the finger print scanner perfectly on the s8 and it would have been a wiggle-stretch on the s8+.
Unlock - Finger print scan (FPS) works well 80-85% of the time for me. I have two scans of my finger and will do one more to see if that makes it even better. Much better hit rate than the horrible Note 7 was, and is easy to find because I have a case on my phone. Face scan is great in good light but *terrible* in low light (never works for me in low light). Iris scan is great in low light and normal light, but I hear it is bad in strong sunlight (haven't tried that one yet). Thing I don't like about iris scan is you still have to hold up your phone a certain distance from your face, and you still have to hit the power button/invisi home button and swipe up to have it work. FPS is just a one-move deal, so I'm glad it works better than it did on the Note 7. I would be hating life if I had the s8+ and had to rely on the FPS.
Buttons - I hate the Bixby and volume button locations. They both needed to be shifted lower on that side, because you simply cannot reach the volume up button one-handed. Terrible. And the damn Bixby is useless right now, so hitting that by mistake brings up the stupid useless Bixby feed.
Screen - Good Lord what a great step up from the 6p. Too be able to read my screen outside in sunlight, ahhh. The only gripe I have is the width, which any narrower would have been a deal breaker. Too many websites don't auto-wrap their text, so you easily end up having to turn the phone into portrait mode to read stuff, especially if you have to pinch-zoom to increase text size. And with my age needing to use readers (sometimes) this is a pain. Screen is also still very tall, even on my s8, so reaching the top with my thumb ain't happening. Edge panels are okay I guess, the screen capture panel is nice to give you those options for screen shots. And no red tint for me.
Camera - Have only taken a couple of pictures so far, so I can't comment. I assume this will produce better pics than my 6p, so that is all I care about. I still need to figure out if I should disable the stock gallery app - I don't want to bork the camera, and I don't know how the camera interacts with the stock gallery. I prefer to use the google photo's app since this back up everything no matter what phone I use.
Overall this seems to be a solid upgrade for me from the 6p. Once I went through the agony of setup and now have everything how I like it, I am good. I know I'll get at least one Android version upgrade (to "O") so I am okay knowing I will lag 6 months behind everyone on Pixels. I don't care about having the latest version of Android like I used to. As long as the battery life doesn't deteriorate, and the phone doesn't start lagging over time, this should last me 2 years until the s10. Still need to get a wireless charging stand (which will be anice upgrade over the 6p) and a better case than this Spigen, but having the s8 will provide me with many more case options than I had with the 6p.