Good stuff, looks like your well on your way.
Competition is stiff though with games like Roswell Fighter being sold at 79c.
but since your using a 3D engine I think you can pull a few nice tricks to stand out (Perspective change as you tilt, barrel rolls at the end of level, or 3D glasses mode seems to be all the rage now).
http://www.pocketgamer.co.uk/r/iPad/Roswell+Fighter+HD/news.asp?c=20525
http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=335319071&mt=8