Great site. But if you're interested in roguelikes I'd suggest starting with Dungeon Crawl: Stone Soup instead (http://crawl.develz.org/wordpress/). Nethack's really showing its age these days and is missing a lot of key features. Crawl is more accessible to newcomers and is less tedious to play. But it is very much a roguelike in the spirit of Nethack.
I agree. NetHack has heritage (and nerd-cred) going for it--but in terms of raw playability, DCSS has it beat, hands-down. Crawl might also be the most active modern roguelike in terms of development (a rotating cast of a dozen+ active developers working consistently over several years), whereas, to my knowledge, all the modern NetHack forks are the works of lone developers.
For players new to roguelikes, I'd also have to recommend DoomRL (http://doom.chaosforge.org/) as a fantastic game, and its shorter length might appeal to more casual players.
Seeing as comments turning into a list of roguelikes:
ADOM is one of the best roguelikes. It's closed source but very deep and high quality.
http://adom.de/
POWDER is a little graphical roguelike targetted at portable game consoles and PDAs. But you can play it from PC. It's reasonably quick and have a very fun and orthogonal skill/spell/item system.
http://www.zincland.com/powder/index.php?pagename=release
TOME (http://www.te4.org) is ADOM-ish (reputedly, haven't seriously played ADOM) and pretty fun. I found the level generation a bit repetitive, though.
I'd like to add that the crawl devteam is really friendly and receptive to patches. Development is very active and I find it tremendously good practice to read a codebase that's been developing for the past 14 years.
Just today the team took a patch of mine to simplify poisoning!
