(Obviously, spoilers for the Mass Effect series follow.)
The bulk of the new dialogue takes place in the final discussion with the Catalyst, the construct which controls the Reapers. In the original ending, he explains why he has the Reapers destroy all technologically advanced organic life in cycles. Then he offers three apparently distinct, but unclear choices: control of the reapers, synthesis between organic and synthetic life, or destruction of the Reapers and synthetics.
Both of these are given more detail and time in the "Extended Cut," which is a significant problem. My issue with the Catalyst wasn't that he didn't explain his history, but rather that he was an almost literal deus ex machina, a small god in a very big box, appearing at the end in order to resolve the apparently unresolvable. He was, in short, the definition of the game putting its mythology above its storytelling.
"Mythology" (often called "lore" in gaming) is a necessary concept for understanding serialized storytelling. It's a vessel for the biggest questions a series has. The modern form of the term originated on The X-Files, where mythology episodes focused on the questions of why a government conspiracy existed to suppress knowledge of extraterrestrials, and what those aliens wanted. Perhaps the most famous example of a storyteller trying to utilize mythology poorly takes place in Star Wars Episode 1: The Phantom Menace, when the Jedi power over the Force is explained as the result of microscopic beings called "midichlorians," an explanation as disliked as it was unnecessary. As a general rule, I find that mythology is an inevitable result of telling stories with multiple installments, but when focused on, it eliminates the emotional core of the narrative and replaces it with a puzzle to be solved – or criticized.
This is what happened to Mass Effect 3. The series' narrative strength throughout was in its character development, and the comprehensible effects of the political forces in the universe. In the Tuchanka sequence in the first half of Mass Effect 3, this all becomes apparent. A cure for the genophage, a disease which crippled the Krogan race, is required by the Krogan in order to ally with the anti-Reaper forces. This forces all the political aspects which demanded the genophage to rise to the fore of the narrative, and they do so via the dialogue and arguments of characters like Mordin Solus, Urdnot Wrex, and the Salarian Dalatrass. The characters, politics, and emotional power combine with intense gameplay to form one of the best sequences in the trilogy, with only the presence of the Reapers hinting at the mythology.
By focusing on the nature and motivations of the Reapers in the end, Mass Effect 3 inadvertently calls attention to the prime structural issue of the series: the Reapers were never the most interesting component of the narrative. Indeed, they never actually make sense within the gameplay of the series. Setting a group of massive spaceships as the primary antagonists of a squad-based shooter/RPG is simply bizarre. Thus it makes sense that the Reapers would, within the moment-to-moment gameplay, threaten Commander Shepard with corrupted denizens of the world: heretical reprogrammed Geth, devolved Protheans, and mockeries of the universe's races in the forms of Husks, Cannibals, Banshees, and more.
This is just one of multiple specific issues, but it's one that effectively demonstrates the problems of mythology-based storytelling. Questions are generally more interesting than answers, and turning those answers into intellectual puzzles means debates over solutions, not celebration of storytelling. What the "Extended Cut" needed was to be a "Shortened Cut," removing the explanations for the Reapers and simply letting them be powerful villains. Mass Effect 3 would have been a stronger story and game without the embodiment of the Catalyst trying to explain everything, without the Reapers' explanation for their motives.
With less time spent on mythology, more could have been spent on emotions. The "Extended Cut" does remedy the specific complaint that the ending of the series resulted in near-genocide, describing the explosions at the mass effect relays as "damaging" instead of the destruction of entire star systems implied by the original ending. This is followed by a series of pictures showing some of the unseen characters from the ending and their new lives. It remedies the issue of ambiguity so many had with the original ending, but it's still largely unnecessary – almost the entirely of Mass Effect 3, other than the scenes at the very beginning and end, was a goodbye to the universe and its characters.
And that's what makes for an excellent finale, which is perhaps the most unfortunate part of the whole ending controversy. Series that focus on character and emotion and relegate mythology or mystery in their endings tend to be more satisfying – in the television world, The Wire, Angel, and Babylon 5 all did this in their excellent finales, but in very different fashion. On the other hand, there are series like Battlestar Galactica or any number of blockbuster films (the Star Wars prequels, Pirates Of The Caribbean, The Matrix) which tried to answer big questions with unsatisfying explanations. Mass Effect 3 was so very close to being worthy of consideration as a fantastic serialized ending, but its apparent need to answer and resolve everything prevented that. An "Extended Cut" couldn't possibly fix an ending whose problem was that there was already too much.
Rowan Kaiser is a freelance writer currently living the Bay Area, who also writes for The A.V. Club, and has been published at Salon, Gamasutra, Kotaku, and more. He still occasionally finds Ultima VI Moongate maps and mantra notes when he visits his parents' house. Follow him on Twitter @rowankaiser.