I know there is already a walkthrough for this game, but it may not adress your specific problems seeing as so many people have unique problems. I've beat the game so if a have a problem just ask and i'll reply to the best of my ability because i've encountered glitches and difficulties but got past them all. Good Luck
one "unch" boss "heart" knock-out: use a highish leveled buzz saw it should kill the red dot as soon as you touch it.
getting higher hit percentage: stay away from automatics and use weapons with a wide spray radius such as the larg shotgun or a 100% hit weapon such as the lightning or chain lightning
having trouble with the bosses that have three sections? try developing your own strategy because you will be facing more of these later in the game, what I try to do is use the big shotgun and kill all of the guns really fast then use rockets to kill the heart, the first section goes in waves so it should be fairly easy, the second and third ones lookrandom but there is a pattern so just stay in a corner where there are less bullets flying through and use you sheild to block the ones that do come by
glitches:
final boss not appearing: there is a simple solution: use the emp blast, for some reason this works, you should only need to try once because this boss is simple
I personally suggest using the chain lighting (if you have it) on the 3 part boss. You don't have to aim which makes things much easier as you will have your hands full dodging missiles and the occasional round of bullets.
