XIII may be the perfect run-of-the-mill First Person Shooter. Everything it does, it does extremely well, and the gameplay is varied to the extent that it keeps things fresh without going overboard trying to make every single mission incredibly different from the last.
There is a good mix of run-and-gun violence, one of the reasons for the mature rating, and also that of stealthy action. Both take an equal amount of skill to pull off, but neither go over the top too often like sending endless waves of mindless goons at you to be mowed down, or making you try to sneak past the same security camera over and over until you find just the right place to hide from it.
The environment around you also plays a crucial role in the action. Guns, grenades, and throwing knives are not your only weapons in this game. Lying around the place will be chairs, shovels, brooms, and even bricks that you can pick up and deliver a single incapacitating blow with. You can also take innocent people hostage whenever the opportunity arises, giving you the option to use non-lethal force to get out of some sticky situations.
The story in XIII, unlike most other FPS's, really helps drive the missions and gives you a clear purpose of why you are embarking on these near suicide runs. The plot is full of political intrigue, sex, humor, unexpected twists, and great characters. Yet it never feels like you're sitting around watching a movie, like in Max Payne or Metal Gear Solid 2. A harmonious balance has been reached between gameplay and story telling. This may be the beginning of interactive graphic novels.
Aside from the Single Player mode, there is also a Multiplayer mode that allows up to six players to go at it online, or you can do a Two Player split screen game with some bots. The Multiplayer aspect isn't all that thrilling, and the unique game type included in the PS2 version of XIII isn't all that great. Stick to the Single Player mode and you'll be all right, just don't look to XIII for its Multiplayer capabilities.