Just got my self a Galaxy S3 and was searching for some good games to try out on it and i cam across CS Portable O.O
Its fun to play (controls will take some getting used too) and not bad considering its free and still a work in progress
Its not a valve game but it has maps like dust 2 etc which is exactly the same, the game is basically like cs 1.6. also has mufti player.

This is the download link http://cs-portable.net/download/android and iOS http://cs-portable.net/en/download/ios