The game is interesting but the moving is a but difficult. If you can, make the spaceship to be controlled with the mouse. It may require some thinking but it will make the game more easy and interesting to play…
This game really reminds me of “Arcadrome”, look it up on the net, it might give you some ideas…
Also, somekind of a bonus cube appearing form time to time would make things a lot more interesting. The bonuses could be: an extra life, a different gun, freezing the enemy guns and you could also include traps like: freezing trap, “20 seconds to win the level or die” trap etc…(Maybe there is a bonus cube but i was too lazy to find out :D, if there is then i apologise…)
Keep it up!
Stefan