Not as fun as I would have hoped.
Quake 4 you play as a Human that will get picked up from the bad guys and then turned into a bad guy too.The idea sounds cooler then it is.Right when you become a bad guy you almost get shot by your friends but then they work with you.The game is a lot shorter then the other Quake games.
The Achievements sound like fun to get but end up being more of a pain to get then they should be.Plus you will not know what ones you have to do to get them.
Multiplayer is fun but is nothing that has not been done before.So a little old and used.
So all and all the game is worth a rental and not a buy unless you are a real fan to the Quake games and even then might not be to your liking.