Sanctum - an FPS/Tower defense game

Sanctum is a game I've discovered through the Yogscast. It's like a mix between a tower defense game and first person shooter, which is a fusion I've never heard of before. Below is the video where the Yogscast tries it out.



I have only tried the demo, but I think it's quite an enjoyable game. The graphics remind me of Portal 2 in a very pleasant way - although, you should note I haven't actually played Portal 2, only watched LPs. The graphics are, at least colour-wise, a bit cartoony compared to many other games, but that's one of the things I like. I like when there are are colors in a game, more than grey, brown and black. I also very much like the music in it, particularly the song in the main menu, which I often start up the game just to listen to.

So, have you tried this game? What's your opinion?