Proven concept needs a little tweaking
Good game overall. But I found a few issues. First off shields are fairly usless in general. They usually take too long to regenerate and can't even withstand one hit without draining completely and allowing damage to the armor. For example, I barely skimmed by a missle of the second boss and wham... dead... the missle didn't explode and I grazed the back end of it. Which bring me up to the next issue. Your collision detection needs work. It's too strict when it comes to money pickup and too leaniant when it comes to enemy collisions. Armor also drains way to quickly and is also useless to a certain extent. Ever played Tyrian? Very good example of this kind of game and play style. Also on the second map you have enemies able to shot to the player when they are off screen and player navigatable areas. It's a good game, just a few pisser-offers...