Underrated shoot'em'ups

Today I was taking a look at my Dreamcast games and came across Zero Gunner 2 again.
For anyone unaware of this game, it's pretty much your basic shmup using helicopters by Psikyo, but with a nifty gimmick: you can change the direction you're facing, much like the PC "Warning Forever".
The first Zero Gunner is apparently emulated in MAME, but I've never played it.
I never really heard much talk about either of them, didn't even heard of the series until 2 came out. It's rather nice and only moderately difficult on normal (with 8 difficulty settings I beleive).

Anyone else familiar with this game or the series?

If anyone else has some shmups they feel are underrated and not talked about enough, feel free to post about them!

>>15

what?! what about BLIND KOREAN GUITAR MAN? his second attack form is uber -- arguably he's even better than Kuga.

also, where're the obligatory mentions of Shanghai Alice and ABA Games? though I want to say that they receive a lot of attention already, I really get the feeling that all shmups are "underrated" and are slowly fading into that little hidden niche market along with Ikaruga and Cave's Mushihime Ultra mode...