Guild of Dungeoneering [Steam store page]
Some of the mechanics are unconventional, but once you learn how to play it properly it's a fun and well balanced dungeon crawler with a twist. It's one of the only rogue-like dungeon crawlers that I actually go back and replay from time to time.

For me this game fell somewhere between Legend of Grimrock and Legend of Grimrock 2 - not quite as good as the open-world of the second game, but Vaporum's voice acting made it more of an engaging experience than the original Grimrock.

The Binding of Isaac [Steam store page]
Decent mechanics but disgusting theme. Enemies can shoot diagonally, you can't. The bad hit-boxes on arrows are frustrating, making yours regularly miss enemies and allowing enemies to occasionally hit you through walls. Made with Flash, low res.

Spiral Knights [Steam store page]
The graphics are cute and the game seems potentially fun, but it lags incredibly bad on my PC - and I'm not sure if it's a problem with the game itself or their servers coping with the player load. Regardless, unplayably laggy even when moving.

This is a fun but easy Diablo style dungeon crawler. It features quick travel via portals and spells, as well as a pet to sell items while you continue killing. Additionally there is a shared chest to transfer valuable items between characters