Interplay declared bankruptcy a few years back, which had pretty much killed any chance of a true sequel. Then, miracle of miracles, they sold the Fallout franchise to Bethesda.
Personally, I expect great things from Bethesda, so long as they keep the plot on track. I did play Morrowind for a while, and enjoyed it...but it did get quite old after a time. I enjoy a good sidequest as much as the next RPG geek, but only if they are diversions from the main quest. Morrowind seemed to be all sidequest and nothing else. Unless I missed something...
Eventually I plan to try Oblivion, but I really don't have the time now.
As for Fallout 3, as long as they keep the atmosphere from the first two games (and don't screw the pooch on the game engine), I'll be happy.