Take Oblivion, put in a series of in-world fast-travel networks like Morrowind rather than that stupid map-based fast travel where you don't even need to have been to a location to travel to it, improve the horse mechanics (every game with horses from here on should just steal the RDR control scheme), add a more interesting and varied main plot, hire more than two voice actors, hire voice actors with something resembling talent, apply the level-scaling only to SOME enemies so some places are actually dangerous in the beginning and you can actually feel powerful occaisionally later on, add more interesting and interconnected social tensions like between the houses, guilds, races, and religions of Morrowind, make more varied use of the mythology and possibly add to it (protip: there's more to the TES mythology than the plane of Oblivion), bring back the elements that were taken out for seemingly no reason (it's not as though polearms required some massive amount of code - all melee weapons in Oblivion are essentially identical), and add more interesting characters that feel less like Generic Quest-Provider #7.
Seem like some pretty easy fixes.