I like where you were going, but man, the colors make me cry inside. the darkness doesn't match the rainbow colors, try adding a black and white gradient on soft light (change the opacity a little if its too much). And the text, not too fond of that font, however, if you erase a little of it and make it look like its behind Riku, it would do wonders.
It's pretty centered obviously, I belive it's a good thing Riku is the first object you eyes will look at. For some reason I feel that the left and right of the sig is missing something.... There's so much in the middle and so little at the corners. I'd want to do something about that, maybe an incredibly weak hint of the swirls to add more balance overall. Just not sure if colour alone is enough to fix it. You be the judge. :>
It's good, but I agree with the other guys who posted... it seems a bit unbalanced, and I'd put a wee bit more stuff in the right side of the pic. Maybe an extra swirl thing or two to even the sides out. And the text was a little hard to read... but I do like the font that you used. Very nice.
I love the concept. The problem is the color manipulation. You actually did a great job on the left, but near Riku, I guess you kind of lost it? Riku's sharpening/er...I guess lighting doesn't go to well with the rest. Great concept, though. ^^
