I've just completed the game with soul collecting.
I got to say it was a lot of fun. The gameplay is simple but cool, and you squashed all the juice out of it with the great level design you made. Graphics were nice, but they need a little more of pollution (I can help you with that if you wish, I know a couple of filters for your textures that would do the job, PM me if you're interested)
You should add a good ghost trophy, for not killing any human to spikes, and a "bad" trophy for killing like 5 humans just for fun (?
The things I disliked are that you can't jump to the left and leave the body you're in and the lack of particles. But I still see the HUGE effort you put on this game. I really say congratulations, it's a great, fun and very complete game. Thanks for making it, I enjoyed it a lot.
PS: Loved the Flixel easter egg in the Comic shop. Is it there any more?