I have 2 things that I hope mostly will get fixed, post your own (doesnt have to be 2) or comment existing
1. Combat system. Lets be honest, it blow monkey nuts in morrowind. Stand in one place, use best attack over and over untill you spam the other guy to death in a volley of identical attacks. I was pretty dissapointed with it myself. Now I know its old news it's getting a total rework, but, it's left some things to ponder on. First, if it is like they say - if it hits, it hits, then what are your chances of hitting, least hurting, a guy in a full plate armor using a small dagger for instance?
2. Stealth system. It was like this: You're in a dark cave. Your stealth is mediocre, an enemy approaches from the other end of the tunnel, you immediatly sneak in the darkest corner. As soon as you see him, he sees you and proceeds to torch/stab/own you.
After some time, your stealth got high. You're walking in a lit hallway and hear footsteps. You see a guard coming in, and start sneaking. The guard and you walk by eachother, he doesnt notice a thing. You come back and start jumping in front of him. Still nothing.
I'm sure the oblivion stealth will be better than that (how hard can it be?) but let's see how they sort lightning out (I hope they add a light-gem or indicator just like in theif as well

).
Infiltrator out.