I'll just have to chime in here.
Shepard dying was certainly a factor that contributed to my feelings towards ME3's ending. I did, after all, make my main Shepard come back in a fan fiction epilogue.
However, thinking back to my response towards the original ending, it wasn't the main factor. The main factor was that the original ending invoked a dark age (not wholesale destruction as some critics claimed, but a dark age of civilization), and thus my character's death failed to achieve what I had set out to do: saving my civilization. Not some nebulous future civilization or "all souls that ever existed" (Javik) nor something even more fundamental like "organic life", but my civilization. As one review put it, the good outcome was removed from anything tangible and relegated to "the realm of far-flung statistics". Shepard died for nothing with which I felt connected.
Then came the EC and removed that particular problem, but compounded another one: the religious vibe around my preferred ending, which - to add insult to injury - made no sense whatsoever lore-wise, flew in the face of all SFnal rationalization and felt like invoked wilfully and artificially.
So yeah, Shepard dying was a raw deal, even suspecting the story was set to end that way early, but on its own it wasn't critical from my POV. The other elements were the critical ones, and Shepard's death compounded the problem.
I felt betrayed by ME3 three times. I could've dealt with one.