Don't forget the abomination of an ending that was Star Ocean 3 or the ending to Rage, which literally made me rage, even more than the ending to Ghostbusters on the NES(dat closing message). Though to be fair, in Ghostbusters case the entire game was awful, it's just that the ending stands out because of the message.
If Mass Effect 3's ending is the worst some people have ever seen then they should be thankful, because they haven't had to see some of the complete hot garbage which some of us have had to endure.
There are many horrible game endings, absolutely, but personally I don't consider anyone near ME3. For a few simple reasons;
1) BioWare never disappointed me in the past. From BG to ME2, even DA2.
2) This was a 5-6 year trilogy. This was not a standalone game. Rage for its **** ending was just that.
3) Many people get very involved when playing the same character for many years. Even more so when they get to decide the characters "morality", love life and personality (to a degree). This was not killing off Lara Croft or Master Chief.
I can understand why the EC satisfied many. If it was standalone game, I think I'd even enjoy it myself. But it wasn't, and quite honestly I think Shepard deserved better. To this day I'm jealous of those who found peace, or even joy with ME3s end.
BTW, since you mention Ghostbusters. Such endings were the norm for most NES games, especially the early ones.