There's only one new release on Xbox LIVE Arcade this week: Chair Entertainment Group's Undertow.
Described as a non-stop action title set underwater, Undertow features multiplayer for up to 16-players over Xbox LIVE or System Link and local multiplayer for two players. You'll be able to play as one of three races (Iron Marine, Nemoidian and Atlantian), each with four unique, upgradeable unit types. These range from the fast and agile to the large and powerful.
In addition to four multiplayer modes, the game features 15 single-player and co-operative campaigns, but it's the fast and frantic multiplayer which is the main selling-point.
For your 800 MS Points you'll also get a bunch of Achievements and 200 Gamerscore Points to earn.