Fantastic
I had a lot of fun with this. Contrary to most criticisms, I think the difficulty level was good and perhaps even leaning towards the easy side (for a fun Hell shooter, anyway.)
I've never actually played anything with this style of control, but it was executed well (by tying bullet speed, enemy movement speed, and displacement together in such a manner that you'll always hit if you know what you're doing). While I tried (and came nowhere near) mastering the tricky displacement controls, I did like that it didn't feel forced: if you only care to use the mouse, you can still get by just fine.
I really liked the hints of creativity I saw throughout. It reminded me just a bit of cave story, which is a very good thing.
Suggestions:
If you pursue another game of this style, could you incorporate a target cycling option? An example would be Q= next counterclockwise, E= next clockwise. It's a basic gripe -- I don't always want to shoot at the nearest enemy.
Anything else would just be wishlist items. More challenges and secrets, weakspots/break-away parts on enemies, and perhaps a little more functionality with the mines (remote detonation? rubberband effects? I dunno, I just felt screwed trying to use them as my only weapon).
I'm looking forward to your next project :D