http://store.steampowered.com/app/91600/

A really fun casual tower defense title from the first person perspective. If you have never played a tower defense game before the objective is to setup a wall of towers between the enemies and your base, they will walk through the maze you have built and be damaged by the towers.

Sanctum takes this a step futher by putting the game into the first person view, after you have built your towers you press enter and begin the wave and the game transforms into a first person shooter. You are given 3 guns. A machine gun which features a grenade as it's secondary fire, a sniper rifle & a freeze gun which you can use to slow one enemy or freeze a group.

In between waves you may upgrade/build towers or choose to upgrade your weapons. Upgrading your weapons lets you deal more damage with the machine gun & sniper rifle, let's you zoom in further and shoot more shots without reloading while using the sniper rifle or freeze enemies for a greater duration with the freeze gun.

There are a number of different towers you can build on your walls. The gatling gun tower good for taking out waves of small enemies, the lightning tower which deals strong damage but takes awhile to recharge and in later upgrades will do a chain lightning attack damaging multiple enemies, the anti-air tower which shoots missiles at air enemies and the mortor tower which shoots powerful bombs at a slow rate to damage groups of tougher enemies. In addition to building towers you may also build & upgrade slow fields to reduce the speed of enemies as they move through your maze.

Multiplayer is tons of fun although in no way competitive due to the use of random waves, the upside is that things are kept fresh and interesting as you don't know what to expect each time you play a map. It features support for up to 4 players, the limit was previously 2 but due to community feedback the developers decided to upgrade it to 4 as well as adding the ability to pool resources between players to upgrade towers.

Each map is beautifully crafted by some talented map designers, there are tons of minute details that you would probably overlook if you weren't searching for them as well as numerous secret areas that help flush out the background story to the game.

The game feels really professionally made considering it is an indie title and is a blast to play. I highly recommend this title to anyone who enjoys tower defense games or first person shooters.