It's a 4 player co-op Diabloesque game with a pretty unique dynamic spell casting system.
In a nutshell, there are 8 elements you can combine to make different spells, like rays, sprays, buffs, debuffs, projectiles, AOE, barriers, mines, and probably lots else I haven't discovered yet. There are swords and staves to pick up with some abilities/+stats but from what I've seen they are not that important to gameplay. There is also no leveling system.
http://www.youtube.com/watch?v=g_XP9OBWGKo - TotalHalibut's review and first impressions. Worth watching to get a better idea what it's like.
Just finished the demo and insta-bought it along with a friend. Anyone who wants to play with us can join our steam group;
http://steamcommunity.com/groups/FUSklansky