Bugs.
Graphics are great, story is great? I can't tell. I have run into a few bugs. The second boss who uses missiles bugged the second time I played through, he didn't fire anything and was unkillable. After dieing on the bomb, which I am convinced had no solution looking at the possible paths (although I might just suck) and the boss glitching, I am really do not feel like going at it again and running into another glitch.
The jumping is very unforgiving especially on stage 2 of the first boss, but nothing wrong with that if you want to make a hard game. No firing while moving also kind of annoying.
The bugs are the real problem, sorry.