Good game ruined by a game killing bug
It may be reacting in some way with my slower computer, but I've never experienced something in similar games that get bogged down. In level four once things start to get slowed down a little every ship on screen begins shooting a incredibly rapid stream of bullets at me. It goes from a dozen or so at once to hundreds and it pretty much kills the game and makes it impossible for me to get past level four.
It's a shame, because it's a fun game up to that point. It's fun and fast paced with a cool style. There seems to be a decent selection of weapons and it's not set up where every new weapon is the only one you'll use, there's actually some strategy involved in choosing one that works for you.