I have not played ME3 and never will (bought ME1 on Steam for $5 on sale a year and a half ago, was bored with it after a couple hours, haven't touched it since) but I have heard there's a ton of rage about the ending, so much so that there's gonna be a new ending from bioware. Can someone tell me how it ends and why exactly it is a bad ending? I don't know anything about the story so explain to me why it ruins the ending so much so that people are raging about it that hard.

1.  It adds a character in the last 5 minutes of the game that is clearly the most impantant character of the IP and then end also removes him.
2. What he says is dumber then most internet rants and less thought out.
2.  Shep just takes what that character says as law.
3.  Changes laws of Mass Effect physics, with space magic.
4. Every ending is basically the same with different colors.
5. The Normandy leave a battle mid fight, grabs your crew from a planet and then runs away because?
6. Out of the 100s of characters you meet and then 10s of sidekicks you get, the ending shows up to 5 of them.
7. Then on top of all that it ends with a moment that says it could have just been a fake story.

[SPOILERS]

It basically boils down to a situation where there are two factors.  The first is that the actions you have taken have no effect on the ending cinematic or any sort of epilogue, and exclusively change the color of a beam of light.  The effects of the different colored lights are negligible in the end-cinematic.

The second is that there are plot holes in the ending and inconsistent themes with the rest of the series.  A major theme, diversity, is completely ignored and actually ridiculed by the endings.  The best ending is rewriting genetic code of everyone so we're all the same, without anyone's permission might I add.  For some reason, your squad which has multiple times risked its life for lesser stakes, is now fleeing the battlefield in the most important battle ever fought.  Squadmates who died from the Reaper laser on Earth are somehow now alive and on the ship which was shown to be fleeing, which makes beyond no sense.  

The "best" solution is exactly what the first villain (Saren) from the first game was trying to accomplish.  The "intelligence" is introduced in the last five minutes, and uses incorrect logic despite necessarily being one of the most intelligent entities in the universe.  You have no option to tell this entity that it's wrong, meaning the devs thought this made sense.  The logic it uses is that machines and organics necessarily cannot coexist peacefully, despite the peace I just brokered between organics and machines ten hours earlier.

And Bioware had to make tons of announcements talking about how certain things don't apply for this ending in order for it to make sense.  Such as how despite that  it was established that the destruction of mass relays would wipe an entire system,  they said "oh, it doesn't apply" for this situation.  Or how logically everyone would starve to death because Earth is nearly destroyed, tech doesn't work and many of the species can't eat Earth food.  "Oh, no one starves to death."

They're gonna come up with quick fixes for the franchise in the dumb cinematic DLC, just like the entire third game is based on the quick fix and poorly written Crucible, which is their get out of jail free card.  Yet, had it been so important, wouldn't the Protheans make the VI on Ilos mention it at least in some capacity in ME1?  How could all of the species possibly contributed over time to a machine that's never been used and that they don't know exactly the function of?

Very disappointing game.  I'll get the DLC since it's free and probably laugh at it because of how nonsensical it'll be.  As for future Bioware purchases, count me out after this and DA2.

By lore when a ME relay goes boom it annihilates the star system its based in (seen in ME2s last DLC).

No matter what decision you make or what you do at the end of ME3 you basically choose the color most of the galaxy will explode in.

This is just one of the many plotholes of the ME3 ending which is beyond retarded and insulting to anyone that enjoyed the series.

Deus ex machina

choices during gameplay basically have very neligible effect on the ending

color coded end decisions

plot holes all over the place

and a general overall disconnect from the rest of the series. It's like the last 10 minutes was designed by someone who had no connection with the rest of the game

There are at least 4 very well done and detailed videos on the subject it only takes like 1 minute to find them; angry joe or the list of 10 reasons etc.

Originally posted by DJJazzy

Deus ex machina

choices during gameplay basically have very neligible effect on the ending

color coded end decisions

plot holes all over the place

and a general overall disconnect from the rest of the series. It's like the last 10 minutes was designed by someone who had no connection with the rest of the game

Yep whole story is one big Deus Ex Machina.  And the funny thing is they also copied the game Deus Ex and have almost the exact same pattern to their ending.  Not only did they use a tired and hacknied dramatic device that almost no one likes, they also copied a game NAMED AFTER that device.

Except that Deus Ex's ending made sense.

The ending summed up in a 4-minute animation.

A 39-minute video that breaks it down into more detail.