Would rate this a solid 4, maybe a 4.5 - haven't gone through all areas yet but it's been plenty of fun. An improvement on the last Bullet Heaven in all aspects; loads smoother, better character/boss/enemy designs... Granted, the character interactions aren't that stellar but I have some nostalgia for them nonetheless, and the gameplay is much more important in most bullet hells imho.
Pulled the score down somewhat because at least two of the achievements seem to be bugged. Namely, I've defeated two of the bosses (1st stage and ice cave boss) without getting hit once, and several of the main levels I've gone through without uing any bomb or getting hit, yet I haven't gotten the "Imperishable" and "Untouched" medals. Not really an achievement hunter as such but it's still annoying.