There's a bunch of great shoot 'em ups for the MD and this is the best horizontal one overall, as well as one of the best period. It's a pretty big leap from the prequel in several ways - The developers had really mastered the MD hardware at this point and their talent and attention to detail is visible throughout every aspect of the game, from the big, tough and intimidating bosses to the varied and detailed levels that can be manually scrolled vertically, to the impressive and catchy soundtrack that somehow mixes metal and jazz fusion tracks in a way that works. I thought the great people at Technosoft overdid it a bit when trying to make up for the low difficulty of the prequel, to the point where some parts require precise memorization and having the special charge-up weapon ready, but it does still take first place in the series for me.
An odd tidbit I can add is that while there's some slowdown here and there, it tends to be built in for effect.