What I hope/expect we'll see ASAP is: settings tweaks (to make the game harder/easier/more realistic/whatever), annoying stuff being removed (we know there will be SOMETHING that'll annoy the hell out of you right out of the starting dungeon...), and redone textures (character & item textures first, then the big world texture overhauls will start coming down the pipe).
New UI is a *must*, and I hope we see one quickly, but it's going to depend on if there's a modder already waiting to take up those reigns or not... could be a bit of a wait. I expect to do my 1st play through with the preschool UI unless it's very easy to alter it myself.
Last but not least, the unofficial patch absolutely can't come out fast enough. With previous TES games as an example, there will be bugs, some will be crippling for many, and some the devs will never bother to fix. Anyone willing to work on an UOP is one very awesome dude/gal.
The one thing I'm not really wanting (even if it should be very easy like in Oblivion) is a mod to remove the compass indicators. I tried that with Oblivion, and there just isn't enough information given in your journal to make up for not having those markers. The lazy quest designers method of not having to actually write details when it comes to main quests perhaps, but with this new Radiant Story generating quests for you, disabling the compass might well make those side quests unplayable. But who knows.