My favourite Roguelike, Dungeon Crawl (specifically the tiles version) jettisons so much baggage that it makes even other Roguelikes look flabby. The premise is as simple as they come: Descend into a dungeon and kill things while searching for the Orb of Zot. There isn't even so much as a town, or any shops along the way, and it makes no concessions to sidequests.
One of the many things I love about Crawl is the persistent levels. Everywhere you've been remains intact when you return, so heading back upwards for a breather isn't a proposition filled with uncertainty. There's a great religion system at work in the game, and after a few levels the player gets to choose which deity to follow. Performing certain actions while praying can incur the wrath or favour of these deities, and each one offers a number of abilities and bonuses - if you keep them sweet.
It's also famously difficult, in fact it's fair to say that the game takes a great deal of pleasure in sending your characters into the afterlife as often and brutally as possible. But you still come back for more. I get wildly excited if a character of mine gets down to double-digit levels in the dungeon.
The tiles version benefits from (obviously) the nice graphical tileset and even mouse control - though it's best to save the mouse for inventory management.
Dungeon Crawl is really a case of wearing the name that fits. It doesn't have any pretention, it just does what it does perfectly. I find it more engrossing and fun than almost any RPG I've played.