I had zero interest in it because of the $15 price until I watched the Totally Rad Show review and frankly hadn't even bothered to DL the demo. Having now been unable to stop playing for the last two hours I have to say this game is as amazing an arcade game as Shadow Complex was.
It is perhaps the most well-paced RPG, downloadable or otherwise, that I've ever played. I love the narrator as a storytelling mechanic. I never get stuck in cutscenes since I am the story. The little quips he makes when I do stupid things like hack down plants for no reason really add a sense of actually being the story instead of just having it told to you.
The gameplay is equally fantastic and the constant upgrades tickle the old collector in me. Unbelievably good game and I feel silly for thinking it wouldn't be worth $15.