Great... but....
I know it's a work in progress but I found a few glitches:
1) You can't crouch and shoot
2) You can't walk and shoot
3) The enemies don't harm you
4) (not sure) Music loops over... probably intentional.
Sorry to be critical and all... I really liked the metal slug series, so I want the best for it. And man, you are SO on your way.