Bought it on a whim today and hot damn, it is way better than I ever expected.
Graphics are still ugly, but not as bad as I thought -- at least it's smooth. The music is FANTASTIC, it's retro corniness embodied, like out of a shooter's soundtrack from the early 90s.
Aesthetically, it doesn't even compare to II. Playing this makes me realize how much I love II, and how fucking beautiful it is (still one of the best looking 2D games if you ask me). Designs are generic, which is a bit of a downer, but the bullets come fast and I love it. The bullets are also hard to see, which is probably my biggest problem with the game.
But as it stands I highly recommend it, it's fun.
It's going to take a while to beat this sucka on a credit.
EDIT: Oh yeah, having more fun with this than any Cave game I've played.