Echoing that Hand of Fate's forward charge is a cheap hit that should be MUCH slower (especially since it isn't made clear that the player moves faster when not shooting), but the boss should also have at least 25% less HP since it spends half the battle on the side you can't shoot at.
You might also want to make it clear that players CAN continue from the level they died at by pushing enter on the title screen after game over. Or, better yet, just have the game over screen say "continue" instead of "press start" and have it go straight from there back to the level instead of stopping by the title screen each time.
By the way, is the game's soundtrack available for download anywhere?