I've been running B4 since it came out and it's pretty fine (although not as good anymore as it was day 1). It did respring once on me yesterday and had a few annoying app crashes (music app is the worst offender when I'm browsing the song queue while airplaying to a bluetooth speaker). The stutter has gotten a bit worse but it usually only lasts a few seconds then it's smooth again.
App Store Updates does seem to get stuck a lot, showing me no new updates even though there are a few (they show up once the phone updated them automatically).
A few random animation issues I guess? Sometimes apps open via the zoom-in animation, other times they slide in from the right. Can't reproduce it at will, but it seems like apps that are in the app switcher sometimes slide in from the right.
The widget screen tends to glitch out the show more/less state of apps (weather widget is always set to expanded but sometimes it's the small version).
Mail app has a permanent "Checking for mail" hint at the bottom and the manual refresh loader gets stuck until I change mail boxes.
3DTouching an app got really laggy the past few days, I'll have to reset and see if it changes anything.
Still not really used to the cover sheet mechanic, I find myself pulling down on the lock screen to check notifications a lot. I see why it's an improvement though, way easier to swipe up to see past notifications than it is to slide down the notification center with bigger phones. Only thing I hate is that reachability no longer allows you to invoke the cover sheet right above the moved down apps (or it's broken here, no clue).
The people / faces are of the photos app has no way to add new faces/people. It seems the only way to add new people is via an individual photo which is a step back imo.
I've reported all issues in the feedback app, there were a few more but I forgot about them.
Battery life is surprisingly good, I had around 30h standby with 7h usage last time I checked at 5%. No unexpected shutdowns when the battery is low, previous iOS betas usually shut down when my battery percentage was below 20% (could've been the 6S battery issue, not sure).