It's an RPG where you run through dungeons and smash mobs up and kill an end boss or two. You can use almost all items/debris/corpses in the map as weapons or projectiles. There are 3 characters released so far with impressively different play styles. You loot stuff. You level up skills. You complete quests. I guess it's sorta like Diablo.
That's about it, but it's surprisingly fun. A group of friends got me started, and I play it quite a bit now. Since it's still in public beta, content is a bit limited at this point, though updates are pretty rapid.