Unreal Tournament is an example of FPS perfection. It has great modes, maps, configuration and add ons. Just great fun.
The game not only has AI in the game which is highly intelligent but it also has incredible visuals (textures, graphics and explosions), sound and design. There are an enormous amount of maps and styles for which to entertain you every need. You can also make your own maps and edit other maps. You can have over 15 players in makes which makes great assaults and CTF battles. Non-stop, heart pounding action is what you can say describes a lot of the epic fights you can have (and also tag-teaming can be fun).
The story is unique in its own right and it is great when you play old foes again in the Tournament. Weapons are great and so is the sound track to the game. Difficulty ranges, but it has a difficulty ('godlike') which is highly hard to beat. Unreal Tournament is definitely up there with great Multiplayer shooters.