I've got well over 1000 hours into Morrowind over several years, and over a dozen characters. I can build a character, and that character will play DIFFERENTLY than the last, because it's difficult to use skills that aren't developed, and your initial build has a strong impact on what you become. I still find new places, still haven't finished a significant portion of the quests, and am occasionall still SURPRISED by things I haven't encountered before, even after all that playing time.
On the other hand, I've got about 80-120 hours sunk into Oblivion, and way more than half of that was extensively modded to try to salvage what I could from the inherently flawed game design. It actually pays NOT to take the skills that the character will use, because of the scaling issue, and the lack of "failure" means that there's no real reason to play one character design differently from another. After a couple of weeks of intensive playing with several characters, it all started to look and feel the same, with no sense of "purpose", and I simply lost interest. Only a sense of "having to finish it" enabled me to force myself to complete the MQ, and I could never muster the ambition to go back to playing it again.
I won't buy Skyrim if the consensus among the "RPG" posters is that the game is more "mainstreamed" and "handholding" than Oblivion. If it's a return to "meaningful" character building and choices, then I'll probably play 2-4 hours a day, 3-5 days a week, for the next several years, as I did with MW, and STILL play at about 10% of that rate after all these years.