And with all of these bosses, there are always those who have beaten them. 
I beat ridley and Bongo first tries    ^^^^ 
now, bosses im sure others beat, yet i had trouble with, was the Arachnid Type boss in Metroid Fusion  
  - Sigma in Mega Man X BUT -  I went through the game and got NO HEALTH pick ups. Pretty tough, but do Able