It sucks. It made some user interfaces worse. Like for example managing your display brightness. You could also activated auto adjustment for brightness by pulling down the menu from the top screen on Android 6.x. This option is now completely gone. Also, home screen drop down menu is now fixed to 6 icons on a row. On Android 6.x you could scroll left and right so you would have more icons on the first row without the need to pull down the menu even further. This was removed. So you have to make more unnecessary steps to go where you want to go.
Also, there seem to be more notifications like, "do you want to close apps to safe battery?" and some more which pop-up repeatedly.
One thing they fixed is the smartview function. Now I can finally display my Smartphone on my old Samsung's Smart TV screen and vice versa without much configuration. Before the update. It didn't work at all, because Samsung broke this feature by patching it.