Gears of War
Could last year's Xbox 360 blockbuster be this year's PC sleeper hit? We think it's too close to call (even with all the extra content that looks like it'll remain PC exclusive). New content that'll be exclusive to the PC version includes three new multiplayer maps, a whole new multiplayer game type, a Game Editor and five new campaign chapters. There's even DirectX 10 support if you plan on playing it at NASA. It's got a great single-player campaign and the multiplayer will keep you going for ages.
More Gears of War on PC is happening over on the game page.