Unfortunately not as fun as it could be because the controls are, well, pretty bad.
Look up key ghosting because you have chosen a control scheme which will "ghost" for nearly everyone except those with expensive keyboards. You should never ever make it so you need to press two arrow keys and any other key at the same time -- this will nearly always result in one of the keys not registering (it's a keyboard hardware thing). Unfortunately this is pretty much the control scheme for the entire game, combined with having to release a key to fire, rather than the far more sensible press key = fire.
What would have been far better:
WASD to move, up/down/left/right to fire in the appropriate direction, and auto-charge while you're not auto-firing. X and C unused.
Maybe not perfect and might still key ghost for some, but certainly would be a lot better than the current controls.