More pop. in cities. The entire Imperial city felt like it was inhabited by 30 people.
While I don't mind the voice acting, I think it's time to hire more voice actors. Too many people share the same voice.
Personally, I felt Marrowind had a more involved and epic story. I liked how it plopped you down in the middle of a small outpost with no clue, in a strange land. You were also treated like an outsider by everyone, so you had to gain people's trust. And the political alignments with the 'Houses' of Marrowind was great. I'd like to see more of that.
Unique 'boss' type characters that don't share a design with any other creatures. I mean, a dragon in a cave or something... I dunno?
Getting to the top of a guild should only be half the journey in guild membership. Seriously, when you are large and in charge of a guild... you should have a lot to do to keep it that way.
Also, maybe make the NPCs have more to say than 4 or 5 preset answers to only 4 or 5 preset questions? Marrowind I had like a gajillion questions I could ask the NPCs. I liked that.
I want to be able to scale walls! I heard you could do that in Daggerfall? Bring it back! Make it a skill or something...
Horse controls really need to be worked on.
More items with unique graphics. It sometimes starts to get annoying finding the same items graphic in every dungeon with just a different effect on them.
And finally, I don't know how things are in Maryland, where Bethesda is located... but here in Chicago we don't walk down the street saying things like "My, my, You look like a sneaky one!" to strangers... especially if they look shady. Nothing the NPCs said in the city streets seemed fluid or like an actual conversation.
NPC1: "Hi, how are you?"
NPC2: "Good."
NPC1:"Did you hear this or that?"
NPC2: "Goodbye!" <--- Let's cut those 'conversations' out of the next game?
And yes, I am nitpicking. Overall, I absolutely love the series, keep up the good work!