I agree for the most part, and I loved the game overall.. i would have happily have settled for all my decisions leading to one outcome, without having to know I can choose this,that or the other door by some random alien backward memory omnipresence that had clearly been grafted into the game to deliver this awkward door mechanic at the end.
I saw the game as a whole as an end, so really this one poorly chosen and implimented game mechanic at the end was a disappointment. (Not the game overall but just this game mechanical device).
I ended up watching all three endings and if truth be told they weren't that 'radically' different, so I'd have been happy if the game had just the nerve to present me with just one ending based on my playthrough as a whole, and drop the whole choose a door mechanic.
Dishonored does it better by judging your actions on your playthrough as a whole to give you 1 of various endings.