The great thing about D&D (that's often lost on people) is that it was a social thing. All your friends get together, kinda like college poker nights (except you're NOT trying to drain the sucker next to you). Best campaign I ever had we were ten kids in a room (on a rainy day), working together, hashing things out. The DM was really prepared, and we got completely immersed and the hours flew by like they do when you're really having fun. It was great.
The fact is, it's just damn hard to get a good campaign together, get a lot of people interested. Probably much harder now because D&D has that (false) anti-social stigma these days, and who needs a DM when you got a computer? D&D takes a lot more work than just firing up WoW (or, for that matter, Zork) by yourself in the basement. Even in the day, if your friends weren't into it, role-playing games kinda suck. On the flip side, if your friends are stoked, your DM puts in the prep-time, and you're all keen to cooperate and work with each other, D&D can make some of the best memories you'll ever have. 'cause it's with your friends.
Most people I know who shit on D&D either never played it, or had a lame experience in a lame campaign. That's a shame, but that's life. Anything involving people, from drama club to Boy Scouts to playing football can leave a bad taste in your mouth if the people in it don't care or are uncooperative assholes.