Morrowind and Oblivion both had their respective strengths and weaknesses. By the looks of it Skyrim is doing it's best to eliminate these past mistakes and combine the good points of past games. Many of Oblivions worst points have already been addressed, thankfully. We've got so many common sense improvements that it makes this a hard question to answer. Improvements like gameplay, voice acting, animation and graphics are just awesome. It truly looks to be a fantastic game from all the information we have.
But with a game this big it's inevitable that some detail will be overlooked, or some game design choice won't be perfect. Which isn't a bad thing, nothing is perfect. Though TES games are about as close as you can get. :hubbahubba:
So what do you think Skyrim's weakness will be?
Personally I'm betting on story. It's also what we know the least about, but I'm left a little scared after Oblivion's hokey bad guys and writing. Still, I hope I'm proved wrong.
Your opinion? : )