The character is too blurred, you want it so that is the main focus. Needs at least one sharpen, keep the blurred background to add a sense of motion. Add a light to dark gradient on the text, make it a little bigger aswell. I'd suggest add more effects but different colours, more colours = more attractive piece.
Personally I think the colors are fine. The sig is just too light overall. That thing between the text needs to go, its too distracting. Also the focal needs to stand out more. Is there something like an exposure layer in gimp? If so add one.
Couldnt change that, thign seperating the text.. im ade it on the stock layer and cant undo.. Anyway, heres another version..
Monotone. Are you using a colour set to overlay/photo filter? both of them are very monotone. . .but saying that, the effects are nice. Just fix the colours.