Gradius
An even more novel idea than introducing real enemy patterns is distinctive Gradius power-up system.
Shmups
Gradius
There are plenty of other changes that had to be made to accommodate for memory limitations of a cartridge in 1986 though.
Mamoru kun wa norowarete shimatta!
While I wouldn’t call this a bullet hell shooter, there are some complex bullet patterns to weave your way around during some of the later bosses. This is where using the curse mechanic can really save you!