As a rookie signature maker, anything that's not a few colors in the background with a picture on top intrigues me, so I'm obviously going to say this looks good, and I honestly mean it. Though, I agree that Sackboy's a bit too dark and that you don't need two of them. Besides that, awesome job, keep up the good work!
If you removed one of the sackboys, the one on the right, it would look better. Also there's some inconsistencies in the white around the words. Art is consistency! Try and make it work. Just fix that and I think you have a good siggy mate.
sackboy is badly rendered (I see the choppy white outline on the big one).
big sackboy on the left ruins the flow. next time I suggest just keeping one focal point, instead of causing 2. 2 focal points = less flow .
logo isn't bad, but I'd move it up a little bit more just for flow reasons.