hey love the first one, I think it's very nicely executed, would blend the outline of the arms a bit more, you can see the erased/pen tool'd area around the outlines, otherwise, first image is pretty pretty.
second image, like was already said, I'd blend the person a bit more and drop a less saturated shadow into the grass, the shadow right now looks a bit too dark. & well text allignment, but that's already been said, so done and done. Idea is nice and with a little work, it will look really good as well.
Third image, I have no complaints, I think it looks really awesome. The colours blend well together, but are also bold, and the squigglies all over the place...well no one can have anything against squigglies.
Fourth image, I think the guy on the hook doesn't look like he's part of the image. Maybe make him a little lighter and more blueish, and again maybe apply a little blur to make him melt into the background more.
Hope that helps, like your stuff. Keep it up.