My five in no particular order:
Shogun Total War: This game has led to an addiction to the TW series.Empire & Age of Empires etc i could never get into.Civilization yes they're ok but this is a game i still like to play.
Half Life 2: Waited so long for this to come out .Forever checking gaming mags for any news...
F.E.A.R.: Love the slow mo in this.Would replay certain levels just for that.At times it scared the crap outa me as i often played in the dark.Late at night.By my self.
Still play it.
Call Of Duty 1,2, but especially Modern Warfare. These games led to my first steps in multiplayer land.Much to the annoyance of my wife
Deus Ex:There's something about this game,I don't know what, that makes me keep going back to it.I love the story & game play.Even though it's beginning to show its age it's another game i reach for.Alot.
yours wecrookie