I still think that the nerd rage is justified. The ending, particularly that "the created will always rebel against the creators" line, is nonsensical. But even if you dispute that, it pisses all over plot details that people who have been really involved will care about. The Geth turn out to be nice. EDI turns out to be nice. The Arrival DLC says that blowing up a Mass Relay wipes out the system it resides in. And... well, there's a magical child who tells you that all the things trying to kill you have been doing so for your own good.
Again, the more you've played of Mass Effect, the more reasons they give you to hate the ending.
Further example: there's that thing in 'The Final Hours of Mass Effect 3' where they've circled "lots of speculation for everyone!". It's like they're saying "We don't know, why don't YOU decide? Answers on a postcard to the usual address". That's not a good ending to any story.