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!

You have to keep in mind that the point of the typical 2d shooter is not to run into bullets and chuck in coins until the game says it's over. Ideally, you're working towards a one-life run. The design philosophy requires a certain combination of reflexes and memorization. This is to varying degrees depending on what you're playing, but both are ALWAYS involved.

Right now I'm playing Castle Shikigami 2 (oh no america-name). I don't know what to think of it. There are a lot of different play styles, but only the very first character is really good. When you play as him, though, you can basically disregard enemies and just bullet-scrape for the entire level. I'll put some time into it, but for bullet-scraping games I like Psyvariar a lot more. Is Psyvariar 2 out for ps2 yet?