When I load into the game, into a dungeon, house, or move around, enemies, NPCs, players and even architecture take forever to load.
This goes from being extremely annoying (ghost cities, missing quest givers, doors, and crafting stations) to being game breaking (being killed by invisible enemies) to sometimes falling through the world.
I can fix this in the immediate area I'm in with /reloadui, but that doesn't help with ambushes or waves of enemies, and having to wait for reload all the time is annoying at best.
Collision still works, as I can run into NPCs, get blocked by hedges, and so on, before they're visible. I did not have this problem at all during the beta weekends and outside of this (absolutely gamebreaking bug) the game actually runs quite well, even at maximum settings.
I know this isn't the only topic on this, but since I haven't seen ZOS acknowledge the problem at all yet, I'll give it a go.