I've bought probably hundreds of RPGs over the years...and none of them offer the replayability and depth that Nethack and other Roguelikes do. Sure, they doesn't have extremely detailed (and hackneyed, rambling) storylines and no graphics at all, but the quality of gameplay is so high I don't even notice.
I was thinking the other day that DUNGEONQUEST is very much like a Roguelike board game.
Without the graphics and what not, nethack has to focus on the game play which is pretty intricate. Plus, you're mind puts in the details that you are not seeing on the screen and sometimes that's more impressive than any graphics. Not to say I don't like graphical games but it seems that many of the better games out there are either older or don't have as good of graphics (WoW being the exception).