Orcs Must Die! [Steam store page]
While not co-op like the sequel, this game has an excellent sense of humor and decently balanced maps. Too bad the humor didn't carry over to Orcs Must Die! 2

The casting system is reasonably intuitive, and the gameplay itself is as fun as Torchlight, though the heavy corridor feel of the levels detracts a bit. There is a smattering of story and humor throughout, but I wouldn't call it story-driven.

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