Sanctum is a Tower Defense game (utilizing the Unreal Engine) from indie developer Coffee Stain Studios. While the mazing, building and upgrading towers, etc. are all similar to what one would expect in a TD game, players are also given a more head-on offensive approach through the FPS portion of the game.
The game can be played in both single-player and 2-player co-op modes (4-player co-op is in the works). The experience is pretty much the same in both modes with minuscule differences; as such, I’ll only really be touching on the co-op experience. There are three maps available (each with adjustable difficulty settings), which are reasonably varied. The map Bridge, for example, gives players a huge grid which enables them to construct any kind of maze they wish, while the map Mine requires strategic placing of towers or blocks to force invaders to run down paths which contain no available building areas.
These guys need to be shot in the back of the head if you want to bring them down
There are two major phases of every stage: the building phase (where players can build and upgrade towers and weapons) and the invasion phase (where the enemies come and players must try to kill them before they reach the core). In the building phase, to build a tower players must first create a block, which does nothing except block off the invaders. This block can be upgraded to one of several towers with different attributes (e.g. anti-air, splash, anti-ground, etc.) A block can also be upgraded to a Televator (teleporter plus elevator), which allows players to port to it from the overhead display. Televators can be invaluable during the invasion phase, as one can port to a spot in front of the enemies and not have to run to catch up to them. Just as with many other TD games, different towers will be more effective on different types of enemies.