Good thing it's free.
The problems with the game are uninspired backdrops, lack of any great weapon power-ups, and the feeling that you've played it before. The graphics would've been pretty good, if they would've used something other than a school bus as inspitration for the ships.
The rate of fire is extremely slow compared to say, the first boss in the game. Your ship does respond rather crisply to any movement of the analog stick, which makes the slow rate of fire stand out even more.
Throughout my time with the game, I have yet to come across a primary weapon upgrade. There are a few secondary weapon upgrades, although one I picked up didn't seem to do anything at all.
The co-op Live play was a bit of a laugh. It was enjoyable with all ships separate, but most want to combine onto one ship, which really just makes the game a bit boring, and frustrating as your comrade proceeds to smash all of you into a boulder, in which case you must find a new match.
All in all, I give it an E for effort. Obnoxious soundtrack, average graphics and sub par gameplay will leave you wanting more. If you are looking for a serious 2D side scrolling shooter, try R-Type.