Heya,
There is no `best.' What you enjoy and what someone else enjoys are two different things. There are people who play Crysis Warhead and think it's the best thing ever. There are a few people out there that actually think Farcry2 is the best thing they've bought this year. There are a few people who absolutely will not ever stop playing Fallout3, for like 6 years or more, until the next Fallout comes out. So take everything with a spoonful of salt. You need to choose for yourself. If a game has a demo, get it, try it.
Dead Space is a great game, worth every penny, replayble and takes major advantage of good audio setups.
Fallout3 is a great game, replayble and has plenty of play time for the single player type who wants a good long game to play on. This game is fantastic, giving you the choice to actually be good/neutral/bad through the game and it effect the game (unlike some where it makes zero difference).
Mass Effect is a great game, not the most replayble game, but has a fantastic single player story and is decently long. Beautiful game and very interesting and enjoyable with team based play or solo missions, etc.
Stalker series are great games. Interesting stories, lots of things to do, very open for a gamer to explore.
Left 4 Dead. The demo goes live worldwide tomorrow. Try it for free. It's a fast paced team shooting game. Very fun, very fast. I'm confident it will be one of the next big "online" games that seemingly never stops being played (like how counterstrike has lasted all these years).
Go to GameSpot.com or something and look at all the PC games available.
Very best,
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