Just few things I can't stand :
01. Notifications won't show on lock screen (missed calls, messages...). Also had the same problem with 10536.
02. Edge has some serious issues with Facebook (website, not an app). I'm unable to attach any image I choose, it just says "Resuming..." and it reloads. Also, when I type a message I need to tap "Send" twice. When I try to click "load more" to see an older messages, again, I need to tap twice. And the last thing : it has some serious issues with copy/paste. Selection of a text is a pain in the ***, and even if I succeed, I'll be unable to paste it.
03. Alarm didn't wake me up this morning. First I thought I didn't hear it, but then I tried again - it just won't work.
04. Some applications are not displeyed correctly and they have some resolution problems (Viber, for example).
05. Instagram won't work (but I guess an app doesn't have a support for W10)
By the way, battery drained quickly, but I solved this issue by activating "Sunlight readability" option in "Extras > Display". Option for "Automatically adjuct display brightness" remained activated (but if you try to change that it just won't turn back to previous state).