Didn't see a thread about it yet (yes, I used the search function. If I'm wrong, I apologize), so thought I'd start it. Sanctum is free on Steam until sunday 1pm PST and 50% off until monday. I don't recall the game being covered here, but it's a combination FPS and Tower Defense. You build towers during building phases between waves (you get as much time as you want, btw, and aren't penalized for taking too long like in Orcs Must Die!) and during waves you shoot the crap out of aliens. They come in many shapes and sizes and you can check types before waves to read about weak spots etc.
I'm assuming the free weekend doesn't include DLC, of which there is quite a lot, but the standard game is also quite good. I should warn anybody who's interested in multiplayer, though. There are griefers and overly opinionated a-holes who will show up in a 4-player public game on like wave 37 and decide the entire maze needs to be done differently. The problem is that sold towers only return 50% of their cost to the player who bought it. So if some asshole griefer shows up and sells all your towers, you can only buy back half. Seriously, play with friends or alone.
And on that note, if you need someone to play with, feel free to ask me. I have the day off from work tomorrow and just bought the new DLC (plus, I can't get DCUO to work), so I'll probably be playing.
TL;DR: Go try Sanctum!
I'm assuming the free weekend doesn't include DLC, of which there is quite a lot, but the standard game is also quite good. I should warn anybody who's interested in multiplayer, though. There are griefers and overly opinionated a-holes who will show up in a 4-player public game on like wave 37 and decide the entire maze needs to be done differently. The problem is that sold towers only return 50% of their cost to the player who bought it. So if some asshole griefer shows up and sells all your towers, you can only buy back half. Seriously, play with friends or alone.
And on that note, if you need someone to play with, feel free to ask me. I have the day off from work tomorrow and just bought the new DLC (plus, I can't get DCUO to work), so I'll probably be playing.
TL;DR: Go try Sanctum!