Do you have fun, creative friends? (Not necessarily unusually gifted people, just folks who can actually tell a story intelligibly and whose ideas and dramatic taste you admire.) If you do, it's pretty easy to have a lot of fun with a pen-and-paper game. If you don't, I think it's going to be a total crapshoot at best -- some people look for strangers to play with and find great new friends, others look for strangers to play with and end up playing boring games with a bunch of boring people who totally don't share their tastes and sensibilities.
There are also lots of pen-and-paper games that aren't D&D. D&D is popular but it's not one-size-fits-all. The main advantage of D&D over other pen-and-paper games is the network effect -- it's easier to find strangers to play with. The current incarnation of D&D is also pretty good if you like team-based tactical combat. If you've enjoyed lots of CRPGs, D&D is likely to be familiar -- there's the same kind of adventures/experience-points/loot cycle driving the game forward. The game's setting elements will also seem familiar, as they have been copied a lot by video games and mass-market paperbacks -- again, good or bad, depending on whether you like that stuff or have gotten really sick of it. All in all, D&D's not a bad choice for a first game (or a second game, or a third game) -- just don't go overboard with buying up supplements and minis right away, don't assume that just because you play D&D means you can't try other stuff, too, and don't be afraid to disregard the advice in the book if it makes something un-fun.
-- Alex
