Game's alright. Not bad, but not even close to Treasure's finest games.
The bosses are great, but everything in between is terribly designed filler. There are a bunch of unavoidable segments, and this is especially bad on the highest difficulty where enemies and their bullets will fill the entire screen.
Sure, you can use weapons with bullet-cancelling properties, but that leads to another issue: weapon (im)balance. Flame + Homing is the winning combination and all you'll ever need to use.
Then there's the score-destroyingly infinite enemy re-spawn. Time limits or temporary re-spawns would have been the right way to go, giving the player a natural incentive to continue moving right (the goal after all, is to clear the game). This doesn't seem like a big deal for the more casual gamer, but for more competitive players score-attacking is out of the question, making speed-runs the only viable form of competition.
With that said, the bosses are exceptional, and they alone keep the game in the 'mediocre' range instead of letting it fall into the 'just bad' category. The soundtrack is decent and the game is visually impressive so those are pluses.
Of course, Treasure learned from their mistakes and went on to develop Alien Soldier, the best game on the Genesis and one of their top 5 titles. Alien Soldier had a proper scoring system, great weapon balance and the non-boss segments were pretty great. For those whore curious, the rest of their top 5 are: Ikaruga, S&P, S&P2, and- wait for it- Radiant Silvergun. That last one is like the best game ever, right?!