Was Ridley actually killed on all of those occasions? Yeah, in Zero Mission, you mess him up badly, but the whole Meta Ridley idea is that he was repaired and implanted with cybernetics. In Prime, after the battle, he falls off a cliff, and no death is witnessed. Same with the first fight in Prime 3, where he falls down the shaft, but does not appear to die. The Omega Ridley fight... well, there is an explosion, but unlike all other bosses, which you see explode, the camera intentionally pans away, and Samus is blinded by the light. Finally, in Super Metroid, I think that is meant to be the game in which he really was killed. He blows up into many, many pieces.
As for Other M, I remember having a good time when I played it back in September of last year. The main issue was the totally overblown scriptwriting, which I did my best to ignore. With that said, I'm definitely not going to go so far, as some others have, as to say that Yoshio Sakamoto should never be involved in Metroid again. He made some blunders in his latest product, sure. However, he factors into the reasons that you are interested in the series in the first place.