I wanted to pick up Quake 4 when it first came out and could not afford it at the time.  I picked it up this weekend and I have not stopped playing it since.  It's freaking great.  One of the better FPS's I have played in a while.  I am about a year late in saying this game is awesome but that is fine.  I picked it up cheap and for $15 bucks it was worth it.