This is not a a discussion about the end of ME3, just the 'fan' reaction.
This has been an idea that's been lingering around the back of mind like a bad smell in a poorly cleaned taxi.
I think most of the backlash was trolling. I'd go as high as 75%
I think a lot of the internet hivemind seems to be on some kind of Bioware hate train, though not without reason, they do have some dubious DLC practices. But then counter to that, internet crybabies couldn't get over that one member of their staff didn't play games and proceeded to attack said staff member online.
Too many people seemed to complete the game in too fast a time which leads me to think a lot of them were pirates who got the game early (Can a pirate have a valid opinion on art? Do they value what they play the same as a paying customer? - somebody should make a topic about that asap) or didn't play through the game fully, instead relying on youtube.
The vast difference between Metacritic user and review scores implies something was 'going on' too, plus Metacritic seems to be an easy target for raging internet trolls. The site has been attacked before. A lot of the user reviews talk about how the game was simplified despite the greater level of depth customization over the second game. More reviews from people who didn't play the game? I think so.
The time spent whining about the game also leads me to believe that it was children over adults making the fuss on the internet.
How many adults have the time to spend so long slandering a game over such a period of time?
How many adults have such unrealistic expectations?
Basically, I think the internet trolled itself into oblivion on this one.