well, i've played through this game multiple times now, and i can understand what they were thinking when they wrote the ending. as i've done a bit of writing in the past, i know firsthand that, as a writer, you don't want the ending to be forgettable. why? because the last impression is a lasting impression. you want something different to happen that deviates from expectations, at least a little.
what Bioware did here, though, almost seems rushed. they can say that they put a lot of time and thought into it, but i beg to differ. IMHO, it feels like they had originally put in that grand and epic ending that we were all expecting, and somewhere towards the end of the dev cycle, a senior level person took a look at it and said, "No, lets do something different where the player has to make one last choice."
as a writer, i'm not opposed to giving the player one last choice as it fits in with the premise of the game. i just would've done it different:
to me, the synthesis choice makes the least amount of sense. sure, every world could've been flooded with nanobots or something to turn organics into partial synthetics, but how do you turn, say the Geth, into a partial organic?? sure you could get creative, but to me it doesn't make sense.
my proposal would be that the Catalyst is actually a "Master" Reaper, or at least the synthetic lifeform that originally created or controlled the Reapers, and it currently controls the Reapers. instead of it seemingly being able to read your mind, just make it access the databases that are likely still inside the Citadel (it is right there, after all) to know who Shepherd is and so on.
for background on the Catalyst, it could be a synthetic that was created by an organic species to help fight off invaders of some kind. once the invaders were destroyed, the synthetic's creators would have some sort of conflict with the synthetics that results in the synthetics starting to systematically wipe out all organic life. the Catalyst, however, opposed the logic that all organics should be destroyed, and it came up with its solution to prevent future organics from creating new synthetics.
the choice would just be destruction or control, same as before. however, the reason a choice needs to be made is simple: the Catalyst lacks emotional insight into how organics feel about its "solution". the Crucible, then, is actually the Catalyst's plan to allow organics to break the cycle.
the destruction choice should remain the same as it seems to be quite logical, and that includes the destruction of EDI and the Geth. the control choice, however, could use some tweaking. my idea is simply this: the control choice transforms Shepherd into the new Catalyst (which, as you remember, still controls the Reapers). this would allow an organic to become a full synthetic and bring an emotional insight into the old Catalyst's solution.
of course, the implications there would be huge if you were either Renegade/Paragon, and i can imagine that a very different ending would take place one way or the other.
anyways, i think that would do more to solve the actual ending than the Extended Cut will. sure, it will be nice to see some more consequences of our previous actions in the ending and bring some closure to some of the characters, but the ending itself is still going to be a bit disappointing.
all that said, i still think that ME3 is the best combination thus far of a 3rd person shooter and an RPG to date. the combat is fantastic, and the RPG elements don't feel stripped down so much like ME2. the characters feel real with a couple of very flat exceptions (still not a Zaeed fan), and the game really tugs at your heartstrings with a number of great moments.
overall, ME3 is one of the best games of all time, but it just falls short in one area: the ending.