Tried one of the games... Not really a fan of the art-style or the characters, to be honest. The gameplay is like a super-hardcore version of Galaga with millions of difficult to dodge shots flying every which way around you. There's a reason why they call it Bullet Hell, I suppose.
It's pretty fun, but not exceptionally so, in my opinion. Definitely worth playing if you like old-school top-down shooters, though.