Well, the Extended Cut is on, just finished playing it and I have to say that I both am and am not disappointed. I'm not disappointed because I never expected it to
really fix things up, and the letdown is because, after all, I had
some slight hope of improvement.
[Spoilers]
Extended Cut doesn't follow the so-called indoctrination theory (which, let's face it, is
the most sensible way of explaining ME3 ending), it basically just provided some additional scenes like snapshots from asari and krogan homeworlds after you disable the Reapers and such. While you can see that Bioware tried to fix some more obvious plotholes, like the radio conversation of "everyone being wiped out" or Anderson reaching the control room before you, their way of repairing the damage is very, well, superficial: they explained the fact that Hackett contacted you onboard the Citadel by showing a short scene when one of his officers brings him a mysterious report and he says something like "Sweet hell, he did it", not to mention that Anderson still beats you to the control room, only now there is more dialogue emphasis on things like "we must have been teleported to different rooms" and the timing is changed a bit, making him say things like "I see the chasm" before Shepard does. Also now "Destroy" shows more clearly and the Geth (best race ever!), EDI and all other synthetics died as a result. And you get the "Breathing in the rubble" short scene even without 100% Galactic Readiness.
There are also some additional lines of dialogue with the Star Child, which, despite clearly being intended as an explanation of sorts, actually make things a bit more confusing (for example the you learn that the Child is, in fact, an AI of sorts and that it's creators decided to become first Reapers..
) and there is one additional ending (apart from the RGB ones), triggered by shooting the Star Child or having the 'refusal' conversation ( "I won't make that decision" and so on), which makes the cycle go on, the Reapers aren't stopped and the civilization is wiped out; afterwards there is a little cutscene with Liara speaking from a beacon like the ones Protheans left, saying that they've failed and all that positive jazz.
[/Spoilers]
All in all I am disappointed - for an almost 2 gB download it added really little and didn't help with fixing most of the obvious plot holes- it's basically a collection of short scenes that serve to expand the existing ending, not to fix it. The only good thing about it is, sadly, that it's free.