The ending of ME3 is broken. Fixing something that is broken is generally regarded as desirable. I don't think it would be an artistic mistake for Bioware to make improvements to their ending. I wouldn't have been able to conceive of having that opinion before I finished ME3, but now that I have I find I can't have any other opinion.
There are many reasons why I feel that ME's ending is broken. Here are some, though by no means all.
1) The ending introduces a new central antagonist in the last ten minutes instead of sticking with, for instance, an already-known antagonist like Harbinger concerning whom the player already has significant feelings. The final antagonist comes from out of the blue and, in some ways, usurps Shepard's role as protagonist, since the final outcome of the ending ultimately depends on the choices it decides to give Shepard.
2) The ending does not allow Shepard to challenge the assertions of this new antagonist, even though a) Shepard has no reason to trust the antagonist, b) Shepard has always been able to challenge these kinds of assertions until now, and c) the stories of many missions and characters up to this point showed the assertions to be false.
3) The one previous instance of the destruction of a mass relay of which we know destroyed the whole solar system in which it resided, yet Shepard has no choice but to destroy all mass relays, inflicting untold destruction on the galaxy. Shepard cannot even point this out, even though we know that (s)he is well aware of it because the franchise dedicated more dialogue to the one previous instance of relay destruction than the last antagonist has in total, over all subjects, and the circumstances in which Shepard began the game came as a direct result of that destruction.
4) The type of "energy" released by the choice Shepard makes, in spite of having three different effects on the Reapers, synthetics, and the galaxy at large, has exactly the same effect on the Normandy.
5) The Normandy being able to pick up characters who were part of Shepard's team on Earth makes no sense. The Normandy even wishing to do so makes no sense; these characters have a mission on Earth, while the Normandy has its own role to play in the battle.
I think I'll leave it there for now and edit the post if I wish to add more.
Just to conclude for the time being, this video [http://www.youtube.com/watch?v=7MlatxLP-xs] does a great job of explaining some of the problems with the ending.