I've only played oblivion so Where do I begin?
I dont like:
Pittyful number of voice actors.
Low resolution textures.
Same body for all races.
Stiff NPCs
Bad Animation.
:nod: I'd forgotten about these.
Give me 1024x1024 connary textures for my armor any day, I'll take that over smaller, but bump-mapped, textures. Bump-mapping is so... I don't know, maybe it can be used to good effect, but it was not implemented well in TESIV, and it looked really tacky and just accentuated the crappy texturing.
The VA thing was also a bad move. VA doesn't go well with tons of dialog. I read faster than people speak, and I don't want to sit five minutes for an NPC to tell me about something when I could read it in 30 seconds. The result is that the brief VA-ed dialog lacks content and does not help paint the world around me.
Same body was boring - even the heads and faces were pretty much the same between all the races. At least in Morrowind the beast races had different bodies. However, the method of scaling a base humanoid body for the humanoid races resulted in some animation errors (bow firing and arrow trajectory, particle effects on weapons, etc). Personally, I'd like to go back to selecting pre-made faces that are distinct for each race.
Stiff bodies and animation hasn't improved overmuch since Morrowind. Thankfully, whatever models and stuff they used in OB is much easier to work with than MW's, so there are plenty of animation replacer mods for OB. I think the jump animation is probably one of the worst OB animations. Walking in MW looked downright painful, same with the arthritic hands. Gamebryo just seems to be rather behind the curve when it comes to good animation quality.