Any game that I get to kill, and mangle people, and blow crap up. Doom would be at the top of my list.
My top three favourite games: 1) Age of Empires Series (esp AoE 2) 2) Heroes of Might and Magic Series (esp HoMM 5) 3) C&C Generals
the best game that i ever play is all the series of GTA or GTA 4 is my favourite game in that series.