Absolutely ridiculous 3rd person shooter that can probably best be described as a 3rd person shooter version of TF2 mixed with Borderlands, but where you create your own guns. Billions of combinations of them. Want a hex barrel rocket launcher with sniper scope that shoots fire? You can do that.
Did I mention that it's completely free to play? Only thing you need real $ for is cosmetic stuff (and faster xp earning, but I find I earn xp plenty quick anyway.) Also, many of the outfits can be unlocked just by playing.