It was a bit unclear what qualified as a direct hit that would kill the enemy by hitting them on the top and what would qualify as a hit that killed me instead... other than that, a bit tough for a first level (took some tries to get it right and kill enemies).
Other than the difficulties above, I did not encounter any real glitches except if you get a bit too carried away and fly offscreen to the top and right (or perhaps the top and left).