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!

I played ZeroGunner 2, and frankly, you could do without this game. Just like your standard coin-up shoot-em-up games, the enemy will kill you, and fast, just to suck more quarters out of you. You're no longer on an arcade machine, but the philosophy hasn't changed... :(

Basically, I was met with infuriatingly fast lasers, showers of bullets, anything to get me trapped with absolutely nowhere to go. If you don't know what the boss is going to do in advance, you'll have literally no way of avoiding some of his attacks.

The same also roughly applies to Mars Matrix, but at least those guys had the wit to include a shield if the situation became desperate.

And of course, Ikaruga did it best by minimizing "trap moves" like that.