Battleblock Theater was a game that caught our attention last year. The multiplayer puzzle-platformer/brawler combined great things like evil cats, a snarky and sinister narrator, and the opportunity to kill friends over and over.
If you didn't experience it last year and you're an Xbox Live Gold member, you can rectify that by acquiring Battleblock Theater at no extra cost. The game's just replaced Gotham City Impostors on Xbox's Games with Gold program, and so it'll stay free to Gold members until the end of the month. To grab it, head on over to the Xbox Games Store.