Lara Croft and the Guardian of Light release date is August 18, 2010 on XBLA. September on PSN, PC via Steam

Lara Croft and the Guardian of Light release date is August 28, 2010
Lara Croft and the Guardian of Light will be released on August 18, 2010 for Xbox Live Arcade, capping off Microsoft’s successful “Summer of Arcade” promotional of top-quality downloadable titles.

The Xbox 360 version of the game will therefore enjoy a two-week or more timed-exclusivity window before hitting the PS3 via the PlayStation Network and PC via Steam in September.

The Guardian of Light is an exciting new chapter in the saga of Lara Croft as a character, and thus is the first title to not carry the “Tomb Raider” brand name alongside it. The game may be a link between the end of Tomb Raider: Underworld, and the start of the upcoming Tomb Raider 9 (working title).

One of the main reasons why this game isn’t being called Tomb Raider, is because the gameplay-style has shifted. This game is a top-down action adventure that features cooperative online and offline play. The game is heavily focused on physics-based puzzle solving that may or may not require two people to solve, and will feature highly detailed graphics and effects to go along with it’s isometric perspective.
Whether playing as Lara or Totec, each has their own special abilities. Lara has a grappling hook which allows her to swing across gaps. And she can help Totec out by shooting out the line which he can balance across. Totec meanwhile has a spear, and he can launch it into a wall which Lara can then swing from or climb up. It’s these type of co-op buddy help situations that are the core of Lara Croft and the Guardian of Light. When playing offline, AI will take control of Totec.

The game also features an advance score system with leaderboard support; Where points are earned by killing enemies, discovering treasure and items, or completing levels quickly. Your scores can then be uploaded to the worldwise leaderboard so you can compete with others for high scores.
When playing co-op (which can be done both locally or online), the second player will take control of Totec.

Lara Croft and the Guardian of Light follows Lara as she goes in search of the Mirror of Smoke, an ancient artifact located in a ruin known as the Temple of Light. When she finally reaches the mirror, she is ambushed by a mercenary army who takes the mirror and release an evil entity. Also awakened by the incident, Totec, The Guardian of Light joins Lara as her unlikely ally to save the world from never-ending darkness.

Here is a trailer showing off footage of this awesome looking action adventure game.

And here is a developer interview that sheds more light on the game.