Spoilers for the endings only.
First off, while the endings are simply expanded on and, despite the writers' initial intentions of not retconning things (which they certainly did), I've come to the conclusion that if Bioware had simply released this game with the extended cut in the first place, it wouldn't have received such a huge backlash.
Why? Because it's somewhat satisfying. The major problems with the initial endings was that the writers wanted to make it as open-ended as possible, but contrary to popular belief, sometimes this intention can be improperly executed, leaving fans confused and ultimately angry. This is what happened in the first endings. Logically they backpedaled, shoeing in the extended cut that is reasonably satisfying.
First off, the war assets play a more shallow, but still worthwhile role in the endings. A high EMS rating can secure the safety of your teammates on the run to the beacon, keep the Crucible from backfiring when choosing the Destroy option, and allow the Normandy to make repairs to blast off after crashing planet-side. The Renegade/Paragon dynamic is used for two different endings in Control, where Shepard could become a benevolent 'god' in the protection of the galaxy or a looming force to be reckoned with. Synthesis, on the other hand, seems to fall wayside from any major gameplay dynamic in this cut, possibly because there's not much to be improved upon it. Though the morally ambiguous nature of it still wages in fan circles and forum boards.
This leads the endings from becoming just three (four if you include the bad Destroy ending) standard pick-a-color-any-color lackluster finales to a great franchise. Wholly undeserved, but if you crunch the numbers correctly with the Extended Cut, that number jumps to seven possible endings without including the slideshow tidbits (ie. the Geth/Quarian conflict, curing/sustaining the Genophage, etc). This includes the new polarizing Refusal ending, Bioware's granted wish to players suspicious of the Catalyst's intentions but with a great cost. While not the 'sixteen' different endings initially promised, it's there. And it's reasonably good regardless, with less plot holes and a satisfying conclusion.
Simply put, these new endings should have been there in the first place. Love it or hate it, at least we are sure that Bioware is listening.