It's friggin' common sense, but, YES, there is a right way and a wrong way to complain or criticize someone, anyone, including a game developer that let you down.
I was one of the many, many people disappointed with ME3's ending, but I certainly didn't act like they personally went out their way to insult my mother or offend me. They screwed up, admitted it, and spent quite a bit of time and money doing the unheard of thing of reworking the entire ending to better please the fans. There were plenty of irrational, and rational, people. I was actually quite pleased that fans sent them cupcakes in red, blue, and green colors. That's clever. That's harmless. That gets the point across in a pretty imaginative and memorable way.
But don't you threaten somebody with death, or threaten their children, or threaten them with rape, or bully and harass them into hiding.
I'm going into this industry right now. I was mentored by a game developer who claimed that nearly 99% of all game developers will screw up their first three games, and most of them then quit before they get around to making the fourth one which people will more likely enjoy. It's long and soul-crushing enough to spend YEARS of your life on something that people throw back in your face and tell you sucks, but it's beyond unreasonable to expect anyone to deal with that amount of stress and pressure in addition to death threats and constant, undeserved harassment.
So, as someone making games right now, I'm sorry gamers of the world, but more than likely my first few games will suck as I learn the ropes and hone my craft. I hope you don't threaten me with rape and murder when I screw up, because I'm really trying to get better.