It was one of the first shooters of the generation to boast a really cool twist. Unfortunately, it just didn't get enough attention at the time. But if you'd still like to try it out, there's one code of which you should be aware...
If you'd like to play as Dr. Aiden Krone in the multiplayer portion of the game, go to "Model" in the multiplayer category and highlight Dr. Krone. Then press triangle and put in the following code- RXYMCPENCJ.