Bethesda could basically make it Oblivion set in Skyrim, and it would still be a good game... but I don't think anyone would want that. Personally I have nothing specific I want to see, I merely want to be impressed.
Consider the giant leap Bethesda took from Daggerfall to Morrowind. Then look at the small step they took (forward or back depending on personal opinion) from Morrowind to Oblivion. There were a few things added but nothing that had a big impact. Better graphics engine, moveable objects, direct physics based combat... and that's about it. Countering that though we lost a variety of weapons, armours, and spells, all the in-game literature was simply recycled, and of course the infamous 8 voice actors. Fallout 3 as well, while you had the Fallout character building system and guns, technically there was little difference from that and Oblivion. That was ok though because it was a Fallout game, the next TES game we need better. Although what Fallout 3 perhaps did do the best, which Skyrim will need to match, is find a happy balance between the Morrowind and the Oblivion crowds.
I don't expect to see the same sort of leep forward we got in Morrowind, but I expect a much larger one than Oblivion got. Give us something new damn it! I mean if you want to look at Oblivion's technical achievements, consider that back in 1999 Ultima IX was released with an open explorable world, the same sort of moveable objects, fully voice acted (and with more than 8 voice actors), and to top it off had zero load times. While it was a very buggy launch that was more due to EA, back in their evil times, pushing the developers to release it when it wasn't ready.