Although the role-reversal concept isn't original, this is the first time I have ever seen it implemented in a shmup. So it is refreshing to that extent.
Using the 'action button' system that you chose, I feel many would have just left the attack to cannons; it was nice to see the missile silos and the ramming posts.
The weak gameplay during the level is forgivable, as this is the first game of its kind (to my knowledge), and it is a difficult concept to work with to good effect. However, the real disappointment, for me, came when I was never given control of a boss. I would like to fly around and unleash my own brand of bullet hell on the audacious hero attacking my space base. This would be especially cool for two player.
I have thought about this inverse concept in a shmup before, but only in passing. Now that I've played such a game, perhaps I will give it more thought. It's definitely a genre approach that requires some thought and experimentation.
Bravo for being the first (again, to my knowledge) to actually develop one of these and throw it out there for play and judgment.
I'm going to review this as a 7/10 under the circumstance that I see it as more of an experiment than a game (as it is a first, and it is rather short). As a game, I would rate it lower.
Seeing that this was submitted in 2004, I don't expect to see another attempt if there hasn't been one already, but I would very much like to see another crack at it. Given the 500+ reviews and 4+ years to think about it, I think you guys have much more to add to this idea.