I'm a real sucker for tower-defense games, although I've only played them as Warcraft III maps or flash games (except Plants vs Zombies). Sanctum takes it all to the next level using modern 3D-graphics together with a touch of FPS-shooting.
Shooting down hordes of units are fun fun fun and it's the reason why Killing Floor and Left 4 Dead are such great games! Here you have the ability to maul them down one by one with your SMG! Now it might be a better idea to combine this with the use of mazing and regular (shooting) towers... but the call is yours!
Sanctum is such a great - and weird - game because of its unique twist to the Tower Defense-genre. This game is wild, so I'm happily looking forward to new mixups! What about Monopoly and Call of Duty? Would be brilliant!