Spec-wise, the Galaxy Note8 is a beast. And day to day performance accurately reflects that. The problem with this device isn't performance per se, it's smoothness, and that's where it doesn't always deliver.
The Samsung Experience UI is definitely miles ahead of the old TouchWiz in this regard, but it's still not the snappiest around and doesn't deliver Google Pixel-like levels of fluency. Although it's undeniably the fastest Samsung smartphone to date, it isn't even as perceptibly fast as some other near-stock Android phones like the OnePlus 5T (or even 3T), not to mention the iPhone - 7, 8 or X.
Speed-wise you'll be fine 99% of the time, but then you will encounter the odd interface stutter here and there. We're talking general phone use activities, where a slowdown or two will show their faces over the course of a day.
If you want a stutter that's always reproducible, just try quickly double tapping the Recents button if you have vibration feedback on for touches. This move will switch between the last two apps you used - akin to Alt+Tab on Windows. Naturally, the phone will vibrate twice, once for each touch of the button. While the first vibration will be nothing special, the second one is always delayed. It's just a small example of a prevalent problem with Samsung's interpretation of Android.
On the other hand, compared to the S8 duo, the Note8 seems to be noticeably faster, despite having the same chipset. In fact it feels like a different phone (for the better) in terms of everyday performance and responsiveness. Maybe that's the extra RAM at work, or perhaps Samsung has just paid a little bit more attention to such details in the Note8.
If you like Google's minimalist view of Android, Samsung's version with its own cartoony UI aesthetic irreversibly stamped over the entire software will not float your boat. Despite what you may read on the internet, no amount of font replacement, stock Google apps, launchers and theming will disguise the fact that you're using Samsung's software. And let's not even mention the weird contour-like navigation buttons and icons.
However, Samsung Experience has, over the years, grown into one of the most feature-rich customization suites to ever run atop Google's mobile operating system. And many of its value-add features have eventually made their way into stock Android as well, their usefulness thus being confirmed by Google itself.
If features are what you're after, the Note8's got plenty of them. If you enjoy making a dive through the Settings menu a day-long activity, then this is certainly the phone for you. Thankfully, Samsung has managed to tone down Settings in recent releases compared to the tab-filled chaos from a few years back. Even so, there's still a lot of stuff in there, including features we're assuming at most 1% of owners ever use (Smart Stay, anyone?).
Samsung's philosophy when it comes to mobile software seems to boil down to "the more options the better", and that's interesting because it comes across as the exact opposite of what Apple has been doing. Yet having loads of options means you're constantly forced to make decisions when you encounter them, and that can actually become quite tiring and annoying.
Case in point: you're on a phone call with another contact on hold, you end the first call, and then the phone asks you if you want to resume the call that was on hold. Why can't it just automatically switch? That's the behavior in Google's version of Android and in 99% of the time it will be what 100% of the users expect to happen.
Samsung's Bluetooth implementation on the Note8 remembers the last used volume level per accessory, so you don't have to adjust that every single time after the phone connects to a speaker. This is one of those small things that can get overlooked but is very nice to have if you use Bluetooth for your music listening needs.
Since the Note8 is similar in size to the S8+, you'd expect it to fit a battery at least as large. But it doesn't, and that's because of the space required for the S Pen. So the Note8 with its slightly bigger screen gets a 3,300 mAh cell, which is nothing to write home about in this day and age (and for a phone with its dimensions). The battery life we've encountered wasn't record-breaking by any stretch of the imagination, but for most people the Note8 should last through an entire day off the charger.
With data connectivity on Wi-Fi only during such a day, we've constantly managed 5 or more hours of screen on time, with auto brightness, Bluetooth always on, and an hour or two of music streaming. The best result in this scenario was just over 6 hours of screen on time by the time the battery hit 8%. When we added in 2-4 hours of 4G use we got down to around 4 hours of screen on time (or a bit more), and we assume that with a 4G-only scenario you'd be even worse off.
Bottom line: if you're even remotely a power user, this isn't one of those phones on which you won't even need to peek at the battery level indicator throughout the day. You will want to do that from time to time, just to be on the safe side. Of course the Note8 has wireless charging support, so when you aren't using it you can just leave it on a pad to top up.
Interestingly, in our day to day experience the Note8 managed to achieve marginally better battery life than the S8+, despite its smaller capacity. It feels around the same in this regard as the Huawei Mate 9 with its mammoth 4,000 mAh cell, so Samsung must have applied some heavy optimizations in this area.