Awesome graphics, amazing atmosphere. Only real downside is that it's really short.

The most fun tower defense game I have played ever!

You've gotta make sure you install a .cfg from the Steampowered forums to make the game run better, but after you do you will have the most beautiful game you have ever played. Apart from a graphical powerhouse it's a great shooter with some good racing elements. The RPG elements are kept to a minimum and are very much simplified so it's more suited towards FPS gamers than RPG gamers, which in my opinion is a great thing.