I like the blend of colors, I does have a 3D look to it. I'm also learning ArtRage. I would probably try adding some color to smooth out some of the black and gray edges. A great piece to experiment with!
You seem to be on the right path. Sometimes your background can help making the top object appear 3D especially if you use the blur feature.
I'm interested to know how you created it. Is it a sticker or another tool...?