From the perspective of someone who has no idea who "Gaara" is (I had to 'google' him

) - it took me a while to distinguish the face of the character, I'm still having a problem with determining the lower half of the face.
I think he blends into the background a little too much. I'd either contrast him more by fading the background colours a little, or use a more discernible render.
I also don't feel like the composition entirely creates a sense of unity. In particular it seems to me as though the white object on the left side of the render doesn't belong in the picture. Of course as I don't really know anything about Naruto (except for what I read in the Wikipedia) it may not just be a random object, but may make sense to fans of the show.
I'm sorry I think I might be giving too much criticism here.

Especially since I'm just a newbie. But I will say I do like harmony in the colours, and the boldness appears to fit the feel of the character (at least other pictures I've seen of him!). And also the textures provide an element of interest and is catching to the eye.
I think you should emphasise the render of Gaara to draw the eyes attention, so that there is a focal point of the piece. Otherwise it can be a little too confusing as there isn't any particular place where the eye comes to rest. If you can do that then the piece would be a lot more attractive.
You have done a pretty good job though, and I am sorry if I appear too forward with my opinion. Feel free to give me a kick up the backside if I have offended you. Especially since I am in no way any expert in the anime/manga genre.