From The TimeSplitters Wiki

Tilesets are Mapmaker tools used for adding the feel of the map. Each game has a few tilesets. Changing the Tileset can greatly affect the feel of the level, for example, in TimeSplitters 2 an Industrial Tile map would look like an old, abandonned factory, while changing it to the Alien Tile would give a clean, space look. Additionally, each tile set has 1 or 2 rooms that completely change their looks depending on the set. The tilesets are

Timesplitters

Alien:A stone shaped area with holograms and ramps. Spaceport:Futuristic Airport with seats and spaceships,very similar to the spaceways map. Industrial:Weapon base with air vents and a missile silo very similar to the level CyberDen. Gothic:A medieval style church with gratings and the large room features Stain glass windows which can be smashed. Virtual:A silver style map with no objects in.

Timesplitters 2

Alien:A clean,bright tileset with laser doors. The only Colours are white and orange. Victorian:A Victorian style tileset this is probably the most popular Tileset in TS2 as it can be used to meet most themes such as Housing,factory's and haunted mansions. Virtual:Similar to the TS1 variety but has blue walls instead of silver ones. Industrial:A dank dirty tileset most likely to be used in sewer and abandoned factory maps.

Timesplitters Future Perfect

Military:A army bunker style map has mine pits and acidic pits. Default vehicle:Jeep Lab:A lab set similar to some of Crow's labs. Default Vehicle:Buggy Horror:A map used in haunted buildings,because of this its use is very limited. Default Vehicle:Jeep Egyptian:A setting full of hieroglyphics and paintings on the walls very similar to the TS1 map Tomb . Default Vehicle:Jeep Virtual:Very similar to the TS2 version but this set has more detail. Default Vehicle:Modified Buggy