Nice, but has some flaws.
it's a good general game, but I think it could use some work. The art and music are great, true. But the controls are a bit annoying, and I dislike the way the upgrade system works. To me, it seems like too complicated and too simple at the same time. I expected more options in the customization, so you could at least do that, or stick to plain old retro-ness. But this seems a little weak.
On a related note, I was somewhat annoyed by how the weapons were set out. Every single weapon that happens to not fire purely in a straight line is on area 3. Everything else is just plain old guns (with a few bonuses later on). And the 'Ghost' gun seems rather pointless. The weapons should be better distributed so that you can use more varied loadouts throughout the game.
Otherwise, it's beautiful, but more should have been spent on gameplay and depth. But it's certainly a good start.