It's actually really fun. It's not nearly as bad as a lot of people make it out to be. Granted, it's obviously no Radiant Silvergun, but it's definitely not below average. I've heard some say it's roughly around Batsugun's area, though I haven't played that one.
I get the feeling that a lot of people judge it based on the PC-98 or Turbo CD versions. The Saturn version is enhanced quite a bit over those versions.
Edit: HOLY CARP, that's expensive! I spent about $75 for it. Jeez, things have shot up way too high.
I remember wanting to get Cotton Boomerang a few years ago and thinking it was too high when it was around $120... look at the prices now. Jeez.