It's a fast-paced mess.
In Quake 4 the main character is a marine by the last name of Kane (our hero from Quake 2). Kane has little personality and people still seem to give him a rough time even though he probably saved all of their lives in the previous installment. For a more in-depth analysis on Kane you can play all of Quake 2 on a bonus disc that is included in the package (It's a whole lot better than Quake 4).
As for the multiplayer, it works. It's not over the top, while it fills the place it needs to. It still contains the basics, death matches, capture the flag, etc. However the real challenge is finding a group of people online who will play you, its virtually deserted out there. Quake 4 is disappointing to say the least, it could have been a lot better but it just doesn't deliver, and it certainly does not live up to the standards of its predecessors.