Ok, first of all I love the feel of it, the movement of the ship is nice, so are the hit detection zones, and as far as the core gameplay mechanics, it's solid.
But, obviously there is much to improve apon:
invulvrability after you get hit, it's a must otherwise a bad move can end the game instantly.
The size proportions of everything, while the current set up is a fun fast paced game, the general hit detection zones, rate of fire and size of projectiles and enemy ships, make it extremly difficult.
Art work could use some work, sounds needed some vareity.
Also power ups would make the game more playable, and have a longer life span... not upgrades just short term power ups maybe... meh