too long; didn't read: get a modchip
Most of the good PS2 shmups (and most of the bad ones, for that matter) have yet to come over to the US. We got Shikigami no Shiro (...sort of) as Mobile Light Force 2, which you can easilly find in your bargin bin for a rockin $10 brand new (if that).
R Type Final seems to be pretty hit n miss for most people. I loved it. Slow, not overly difficult, but still challenging. Lots of replay value (
GOTTA COLLECT 'EM ALL) with some pretty awesome alternate stages and customization options. It's no R Type Delta, but it's good.
But some of the best shit never came over here. Dodonpachi Daioujou redefines pain. I fucking love it. Fire that baby up for a few credits and then go play ANYTHING else, and whatever you're playing is suddenly a hell of a lot easier and slower paced. Bullet hell, pure and simple. I can't recommend it enough :)
ESPGaluda, on the other hand, initially looks impossible but turns out to be Cave's easiest shmup that I've played (never played Ketsui, which I've heard wasn't too hard either). It's sort of the sequel to ESPRade, but there's this weird gender changing aspect...yea...uh... you just need to play it. Rockin' soundtrack, great level designs and boss / midboss designs, and there's an arranged mode that's nice and hard. Not Dodonpachi Daioujou Black Label hard, but still pretty difficult :)
Psyvariar Complete (contains Psyvariar Medium Unit and Revision) is enjoyable but very, very short. The purpose of the game is more of a scoring exercise than anything. If you're playing to 1 credit clear the game, don't bother with it. It's all about balls as you try to buzz all of the bullets you can, leveling up the shit out of your ship. The sequel on Dreamcast is even better imo.
Shikigami no Shiro 2 should be coming out in the US pretty soon as a budget title, but you could always import it as well. I haven't played this one, but I heard it was the worst of the SnS2 ports (it came out on GC, PS2, Xbox, and DC in Japan; i only own the DC special edition). I dug it on DC though..so...yea..i'll be picking up the budget release whenever it comes out.
Gunbird I and II and Strikers 1945 I and II are both available right now. You could play 'em in MAME if you wanted *Shrug* The console conversions are arcade perfect and worth picking up if you dig Psikyo's goodness.
Shienryu got released as a budget title with its terribly bland sequel (which was originally planned to be a DC game but got cancelled). If you've ever played Daioh in MAME, Shienryu is basically a heavilly upgraded version of it. The Saturn version was arcade perfect, but the Playstation versions had assloads of slowdown. the PS2 version is arade perfect, but IIRC it doesn't include all of the extra modes from the playstation versions. Still, for 2000 yen it's a killer deal. Watch out for that sequel though..it's pretty damn bad.
XII Stag sucks. I'm warning you, stay the fuck away. If there's one reason why the GNet hardware needs to be emulated right now, it's so that everyone can see just how bad the game is and avoid paying 5800 fucking yen for the god damn thing. Jesus christ. I wish i had never bought it.
Fantasy Zone will be coming out in the US on the Sega Ages disc along with 9 other games, and it's going to be $20, IIRC. Virtua Racing Flat Out will be on the disc as well, so if you don't pick it up I'm going to monkey stomp your fucking eyes through the back of your head :( (watch out for those changed physics in Virtua Racing though...it's more like Virtua Daytona now. It's not bad, just different). Golden Axe is also on the disc, and it sucks new york hardcore. You need to play it just so that you can appreciate all of the good games more.
the Space Invaders 25th anniversary collection is a rip off. Avoid it. It doesn't have Space Invaders 91 or 95 on it, so it's really more like a Space Invader 5 year anniversary pack or some such. Fucking Taito.
Star Soldier isn't terrible, it's just seriously retro. and slow.
Choaniki sucks as much as every other game in the series. If you simply must play it, just buy the playstation budget rerelease for 1000-1500yen