I read an article describing the top 5 games of all time, but most of them are pretty obscure. So here are my top 10 games of all time, in no particular order.
Super Smash Bros.
Unreal Tournament 2004
Command & Conquer: Generals: Zero Hour
Command & Conquer: Red Alert 2: Yuri's Revenge
There are so many other good ones, but these are the ones I really enjoyed playing (and some I still play).