A great but underrated FPS
There are two game modes on the Gamecube version. Those being the single player campaign mode and 1-4 player multiplayer mode.
The campaign mode is very well done puts you in control of someone with amnesia who is accused of assasinating the President. It's your job to piece the puzzle together and uncover the truth. This mode is very entertaining and is generally quite easy. There are some hard parts but not that often.
The multiplayer mode is definately the best part of this game. You can have up to 3 other players with or without bots or you can choose to play on your own with just the bots. There are a few game types including Deathmatch, Team Deathmatch, Capture the flag and hunt. While the first 3 game types are obvious, the 4th may not be. Hunt is you chasing a ghost type character. The object is to kill it. It can kill you instantly by walking in to you and it is quite a challenge, especially when you are playing with bots or other human players.
The gameplay and controls are generally straight forward and simple. You have your standard moving, aiming, shooting, jumping and crouching and a few other features to the game mechanics. The controls are pretty intuitive but may take some time to get used to. The game's AI is a bit dumb in some parts but mostly ok.
The graphics, in my opinion are great. As mentioned before they are cel-shaded. This is a semi realistic but mostly cartoony style and really works well. There is a lot of detail to the environments, Characters, weapons and everything in between.
There is nothing very distinct about the sounds. I can't remember ever hearing music during multiplayer but different sounds like explosions, gunfire, etc are done well. Voice overs could have been done better but they do the job.
Overall this is a very good game and despite what some reviews say, it is definately worth picking up, especially now seeing how cheap you can get it.