I like D&D as a game/genre because (1) lots of people put out things for it; so much so that there is bound to be something I will like in there, (2) I find it easier to find players, (3) I think it's a good balance of quick easy rules and detailed game play.
I can't say I've ever hated a game system, but there have been many many times I disliked D&D up until the current version. The obscure and sometimes contradictory rules. No real way to make magic items. No skills (even proficiencies don't really count). Fire-and-Forget magic. Special exceptions made for so many things. Other stuff shoehorned in backwards or sideways, like unarmed combat. So many game systems in the 80's and 90's surpassed D&D in clarity, playability, and state-of-the-art rules that I'm honestly surprised it's still around.
OD&D was OK, but most of the games I played in were so heavily house-ruled that we might as well have been playing a different game everytime we sat down to the table. But for the most part we just didn't know any better.
AD&D 1E was OK and we had a lot of fun with it, but again with the house-ruling and arguements about rules. By the mid-80's we'd still play it sometimes but we generally played other things at least as often.
I can't really speak as to the red/blue/whatever boxed set versions: I never knew anyone that played using those rules alone. By then we were into AD&D and the concept of races as classes was just too much backpeddling for most people to take. We used a lot of the modules, though.
AD&D 2E was a good improvement, I thought. Not nearly the improvement it should have been, but good enough. We didn't have as many house-rules. But there was a real sense of 'too little, too late' after awhile. After a few years, the thought was basically 'Well, at least it's not 1E'. There was a lot of stuff coming out for it but I didn't pay much attention to it; it wasn't what I wanted to buy. By this time, most of us were playing Vampire or other WoD games, HERO, and a little GURPS with the occassional RuneQuest or Traveller or some other system. We still played AD&D from time to time but it wasn't the number one favorite.
So what kept us playing it all those years, even with better game systems out there?
Players. D&D was nobody's favorite game. But it was everybody's third or fourth choice. So to get a large viable player base, we went with that a lot more than we might have done so if more people could have agreed on something else to play.
3E brought everyone I know back to D&D. We've played it or a d20-related game almost exclusively since June or so of 2000, when we finally had enough hints to begin playing 3E (including a huge document from EN's original site).
