Add music, pauses between the waves, and a little enemy variety. Everyone just shoots you(well, some explode too). You could possibly make the ship a little more pretty. Gameplay gets a little repetetive, try to add different types of weapons(seeker missiles, bombs etc.). But overall, it's OK for being a first game.
Also, a few more things, you didn't make the game so long it got repetitive, the level design(I can call it that right?) was very good, the two bosses were just like a boss should be, epic, hard, and not that hard when you've got a strategy. Overall I wonder if I should give it a five instead...
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