My turn:
I started with ADOM about four years ago, after having found it in some free game download site, in a fit of boredom. Since I'm really into the innerworkings of progamming and computer mechanics myself, and the game initially appeared to be something that required a lot of knowledge in that field, I was put off. But when I realized about how intriguing the game seemed after reading through the manual and some other resources, I tried it again and got a bit hooked. It was a lot of fun, and paved the way for an appreciation of roguelikes in general.
Then I moved to Dungeon Crawl, by which time I was very into roguelikes. The variety in races and classes truly fascinated me, so I kept at it and had some success. Nethack was next, but the problem was that reading the spoilers and learning about all the intricacies of the game was a bit more fun than the game in practice, at least the middle and the end of the game. But I still can enjoy a few rounds of Nethack and can pretty reliably get down to the quest at least.
I stuck with those three, until I discovered the newsgroups, and it was no going back after that. Commercial videogames started to lose my interest, and I started enjoying 7DRLs and various other smaller projects. DooMRL, POWDER, Angband, Ragnarok, and several others got some attention in this time period but nothing too extensive.
Then recently, I picked up ToME, which was a case similar to Nethack, and had a roguelike renaissance, so to speak, where I got back into roguelikes hardcore. And here I am, loving Mage Guild!