This game is one of the great open-source game success stories IMHO. The community has come together to make a game that is technically impressive, while not becoming diluted by design-by-committee to the point of becoming "a mile wide and an inch deep".
Oh god, I love Crawl. It was the only game I played for like a year. I stopped once I ascended with every race and every class (at the time) at least once. I'm tempted to return...