Plusses and minuses, positives and negatives.....
I LOVE the notification handling. So superior to everything else it's not even close. I'd pay plenty for an app that brought these capabilities to my phone.
The fingerprint scanner is WAY faster now. Essentially instantaneous.
I hate the loss of the regular Samsung settings toggles and the ability to customize the toggles that are shown. Standard Android is a giant step backwards here. Fewer toggles, and no choice as to what ones are shown: how can anyone consider that an improvement? Only Googlely fan-boys who think any that comes out of Google is automatically superior.
I've come to like the recent apps screen, although the animation is a bit much. With "stock" Android, you can only fully see the one card at a time, and after a few days the stack of cards is so long it's a nightmare to find anything. It's actually easier to recognize an app icon than the glimpse of a screenshot as you scroll through cards, and I can find what I'm looking for faster with this approach than with cards..
On screen widgets are, yet again, stupidly implemented. Let me put a widget ON THE LOCK SCREEN, not on a hidden screen that I need to scroll to. With a fingerprint scanner it's easier to unlock the phone than to display a hidden lock screen. I'm not using this option at all. (Widget Locker got this right 4 or 5 years ago, but sadly doesn't seem to work on Marshmallow. Why can't Google and Samsung figure this out?)
On screen apps aren't quite as useless. You can swipe on an icon, then use the fingerprint scanner to open it, but it's at least as easy, and probably faster, to just use the fingerprint scanner to unlock the phone. And I'm not sure why a tap on the icon forces you to use a pin, while a swipe lets you use the scanner. Why not default to the scanner on a tap, too? It would be nice if you could open these apps without unlocking the phone, but be locked out of anything BUT that app (sort of like pinning). Again, Widget Locker got this right.
In spite of what some seem to think, the color scheme can be modified, and made pretty neutral and reasonable in settings. I'd like more granular control, but what's there is tolerable. You can also set your own lockscreen wallpaper.
On balance, I like it. It's clearly a work in progress, but notification handling alone is worth it.
Unfortunately, I've had to uninstall it. It's too buggy to be my daily driver. The home button doesn't always work, sometimes requiring two taps, occasionally not working at all. Sometimes tapping on a notification doesn't do anything at all. But when it works, the notification capabilities are brilliant, Brilliant, I say! I'm already missing it.