Giga Wing 2
If you're into crazy bullet-heavy shooters, this is your dream game. It has a nice story, absolutely stunning gfx effects and ridiculously high scores, billions, trillions, gazillions, you get the picture... weapon system is nice, you have a standard expandable weapon, a smart bomb and either a energy barrier that can be used to deflect bullets and destroy enemies/installations with it, or a laser barrier that auto-kills enemies. If you play the game for score, it becomes very challenging, even more so due to the mean bonus system that, apart from giving you lotsa points, resets your score multiplier once you use a smart bomb... Quite underrated game IMO.
Gunbird II
Pretty basic shooter with a funny/anime-ish theme. IMO, the developers played too much Sonic Wings and Strikers before desiging this one, there are many similarties but it would be wrong to call it a clone or something, it's actually very entertaining if you want to one-credit it. Some ppl also like the zany pics and bits of "story" between the missions.
Mars Matrix
One of the best DC shooters IMO, also by Takumi (the Giga Wing guys). It has a unique shop system with lots of items that keeps you coming back for more, decent tho not really awesome graphics and music. Gameplay shines, the weapon system consists of an upgradable main shot, a armor-piercing blast, a chargeable smart bomb combined with a bullet-sucking-and-spitting feature similar to Giga Wing 2 but much more refined IMO, and finally a rotating razor blade for close combat (basically another feature of the charge super). In fact, the bullet-sucking and hitting is the core of the game, and once you master it, the crazy amounts of bullets that fly by suddenly make sense. The bonus system consists of small-to-huge gems that the enemies leave behind, these gems also update the main weapon. In the shop, you can unlock extras like galleries for the credits you get by beating the game or single levels or reaching a certain score, and not only that but also additional gameplay features, extra continues, extra lives, different ship colors, vids of perfect games and gameplay tips, etc. That and the many different basic play modes give the game tons of replay value. Very cool if played for score.
Zero Gunner 2
Good-looking Psikyo shooter with nice gameplay features and good "mecha" graphics. By holding B or X, you can set a turn marker and rotate your ship around it to attack enemies that sneak in from behind. If you're not shooting, your ship sucks in crystals that the enemy ships drop. This charges an energy bar that can be used to activate super attacks that vary from ship to ship. Not an easy game, but anyway, a good candidate for a one-credit finish. The game doesn't really offer any mind-smashing surprises or really innovative features, but it's really big fun and plays very smoothly.
)...