Game I play regularly:
Counter Strike Source (especially gungame with instant respawn)
Games I have (re)played in the past few months or games I play occasionally:
Portal
Crysis & Crysis Warhead
Roller Coaster Tycoon 1, 2, 3
Need for Speed Series (especially Most Wanted)
I am also thinking about getting Burnout Paradise Ultimate Box.
How is Call of Duty World at War? Hopefully Modern Warfare 2 will be at least as good as COD4 was. The previews I have seen for it look great. I had a fun time beating the COD4 Epilogue on Veteran with knife only
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http://www.xfire.com/video/bd570/ )