Does anyone remember a PC bullet hell game, I think it had "Raptor" and lots of purple bullets. It had SNES graphics and what was fun was the absolute bullet-hell, there were just tons of bullets to dodge.
Mechanically, rRootage takes 4 popular bullet-hell mechanics (Lasers + Bombs, Ikaruga, Bullet "grazing (a close dodge)" to build up super meter") & one more.. and gives you dozens of levels in each mechanic.
http://www.asahi-net.or.jp/~cs8k-cyu/games/ABA also created BulletML, a Bullet markup language for describing Bullet patterns. There's a unity asset store BulletML scripter somewhere, too.
A trick a number of SHMUPs use is to make the player's hurtbox smaller than their actual drawing so the player can dodge better. Some games show the actual hitbox as a rectangle in the middle of the ship.