It seems the developers have found a way to keep customers from noticing this game has no multiplayer capabilities at all, (in the true sense of the word.) Even Arnor, from what I understand, is just choose who you want to play a metaverse game "against" and then after both players have finished their "own" game the winner is the one with the highest score. I hope I'm wrong about that because everyone can do that right now without having a programmer tell the code to tell us how our scores compare.
If mega events are going to be realistic they need to be realistic. A futuristic space traveling society is not going to all of a sudden loose planets, even a bunch of minor ones, to a very sudden uprising. Give the player some sort of information that something weird is going on some turns before everyone in the civilization gets assimilated. And add an objective to complete to prevent or diminish the impact; dependent on how well the objective is met.
Devs, people who play games are used to rules. And manuals. This is a space strategy game so customers get frustrated when they are playing according to 4x space strategy "rules" (which were laid down by the Master of Orion series, like it or not) and all of a sudden the laws of physics governing their existence in the game change; (so to speak.) People invest time from their real lives in games. When something this outrageous happens and your customers have spent time out of their actual lives to play your game it doesn't leave them with a good feeling about how they have spent their time. It was a waste.
One of the reasons people play first person shooters is they feel like they accomplish something. They know how to accomplish something within the game. I'm not saying it is the main reason.
Players are also used to an instruction book with the game. Basically people who are upset with what's going on are upset because they don't know what is required of them to win or accomplish their goals. They are doing great and think they have the hang of it and all of a sudden BOOM!! They realize it was all for nothing.
Dev's if you don't want to fix mega events according to your customer's suggestions then don't call them mega events. Your customer's see the "mega event" check box as a game option to include random events that can be devastating or good to all civs in the game. Not just aimed at the way a player plays. Without a manual how are new customers supposed to know what you mean when in previous 4x strategy games they are used to it being different from what you've done. Just change the words to "Advanced Play." And have some sort of instructions in the forums or, heaven forbid, a manual that explains this option is aimed at making the player squirm until they decide to devote as much of their real lives to it as they need to in order to beat it. There are people that expect a manual, even in electronic format with the download or on the CD or DVD. People go to the games forums and vent when they are frustrated and stuff is wrong.
From my limited view of the world those who totally hate this game state it is a messed up version of MOO2 or compared to something else that is similar. This game is not MOO2. It's much better.

The rules have been changed and a new precedent has been set but for some the word isn't getting around. Documentation would fix this, I believe. Those who rant on the forums like the game and want it fixed because it is messed up from their perspective, or they feel cheated out of time and money and want the whole world to know it. I would think those who are upset enough to not play anymore don't even bother to post and just sell the game on the internet.