A lot of good ideas here. I think the art style works mostly with a couple of objects that were hard to decipher (like the portals to areas). My biggest gripe with this is that the bullets are difficult to use. They don't go very far, it's difficult to aim, and they don't last for very long. And combine that with the fact that there's a hefty cooldown between each shot means this is more diffcult then it needs to be.
I'd say fix that piece and this would be a really solid title.