Looks like our payment for the recent Xbox Live downtime will be a game called Undertow, a 'fast-paced, action-shooter'. The title normally retails for 800 Microsoft Points.

Official Release:
Developed by Chair Entertainment Group, Undertow is one of the highest-rated and best looking games available on Arcade. Undertow redefines aquatic based shooters through a mix of high-definition graphics, intuitive controls and multiple modes of game play action. The game features a full story driven-single player campaign, on and offline co-op, and multiplayer for 2-16 players over Xbox LIVE for Gold subscribers. Players battle for control of the oceans as one of three selectable races, each with four unique, upgradeable units. 'Undertow' is available worldwide (normally 800 Microsoft Points) and is rated E10+.
(full release at source)

Gameplay Footage:

JelalTrueshot via gamingshogun.com »