If you like run and gun FPS's then you will definitely love this game.
Quake 4 is a continuation of the war against the alien race known as the Strogg. The game has you playing in the shoes of a marine named Mathew Kane who is a "certified badass". As one would expect, Kane kills and kills his way to the end of the game. The campaing is very run and gun, no holds barred action. Most of the game is spent blasting aliens although there is some light platforming involved but it is never boring or repetitive. Also during the course of the campain are sections in which you take control of vehicles. These sequences really get your adrenaline flowing as they are very fast paced and feature a lot of action. Another thing to note about the campaingn is that it is fairly legthy, clocking in at about 10-15 hours which is great for a game like this.
On the multiplayer side, if you like straight balls to the wall deathmatch, this is your game. The action is fast paced and it is easy to jump into an enjoable online game. The Gamespot review complained about old "1999" mutiplayer but its still fun as all hell.
The graphics are great if you have the system for them. On my Athlon 64 3500+, 6600GT, 1 Gig ram, this game looks great. It runs ib hight at 1024*768 resolution smooth as butter with only only some minor hicups. The game also sounds great. The sounds for the guns are awesome particularly the machine gun. All guns sound powerful and give you the feeling that you are actually wielding these powerful guns.
All in all this is a fantastic game. If you like run and gun FPS's then you will definitely love this game. It is a must buy if you have a good computer and like FPS.