I've got it as part of Half-Life "The Orange Box" on the Xbox360, it's only a single player game and if you stick at it you'll finish it with a day a two, it's nothing like Half-Life so beware, it's a puzzle game with a brilliant sense of humour.
Brilliant, if extremely short game. The ending is great. If you have it on PC and want more, you can grab the Flash Map Pack and add another 40 levels but I warn you, they get damn hard!