The problem is that we did get so much good from the ME series that when it ended up boiling down to a simple A/B/C choice, which was not what the series conclusion was supposed to be like, it disappointed many fans who had come to expect so much more from the franchise. No one complains about the endings of games where the player is not presented with choice, because the game was heading towards its scripted conclusion and there was nothing the player could do to change or even affect it.
With ME, players were given such an immersive experience where decisions expanded and carried over throughout an entire trilogy (which I don’t think had been done before on such a scale) and to get an ending where not only are there sizeable plot holes, which so far have not been explained, but decisions, one of ME’s foundational aspects, are also taken away and made for the player by some deus ex that is not telegraphed in any way, shape or form in the trilogy left some players wondering why BW bothered with choice if in the end it didn’t matter and they could not create an ending that in some way felt logical to the way they played their individual games.
In a game created where choice and decisions mattered so much, the developers should recognize that, while they may have a specific ending in mind as their own personal, artistic statement, they also must see that not all players may share that same and that in their decision to give the players such control over the events that occur in their own ME universe, they should have created an number of outcomes that cover the various paths down which a player could guide their Shepard.
This all could all change though with their new content initiatives : plot holes explained or solved, additional, not replacement, outcomes implemented, and resolution granted for those seeking it. If you are happy with the way the game ends, then you got what you were looking for, but for many of us, there was nothing there at the ending of things that resembled the game that we have loved so dearly.