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as the beginning does not engage me in any way, why should I care for the ending?
watching a serie just for the finale is not a very compelling reason

It's a compelling reason if the entire story is built around the ending. The original manga is famous because of the ending, among other things.

I don't care about the manga, by you own description it was famous only because it was shocking not necessarily because it was a good story, a good writer can engage you from the beginning, don't you think?

I'm not going to buy the promise of some fantastic ending if you can't even pull a decent start... (it don't even promise me that fantastic ending at the beginning to at least try to hook me with it...)

I rather rewatch Hellsing or Berserk or Eva or whatever else that was inspired by it