(continual disclaimer: I still haven't played ME3)
It flabbergasts me that the ending sequence of ME3 (not even the ending, just the pre-ending sequence) apparently doesn't demonstrate a wide variance based on all of the work you've been doing up until then. That was like one of the best parts of ME2. That was one of the only things I liked about ME2!
absolutely
the me2 ending, despite being kind of shitty plot wise with the human reaper or whatever, was mechanically pretty evocative of its narrative
the entire game was about recruiting people, and gaining their trust and loyalty so that they would go on this crazy suicide mission with you. if you did not do well enough in earning this trust, the mission could fail
once you're at the final mission, you see the impact of the choices you made in acquiring squadmates/earning their loyalty. only some guys can do some things, and if you don't have their respect as a commander, the whole thing can go to hell.
but not only are you witnessing the impacts of your previous choices, you get to make a whole host of new choices which directly impact the ending, and which you make based on what you've experienced throughout the game. you know who your best biotics are if you've done their story missions, you know who your best hackers are, you know mordin should probably retreat with the civilians, etc. if you get this wrong you're a shitty commander. it also allowed you to finally escape the fact that the entire game has you using only two squadmate out of a billions. for the first time in the series, you really need everyone, and use everyone, in order to survive. the ending validates spending time getting squadmates you never use through normal gameplay, because you will need them at the end.
mass effect 3 literally does none of this, not with your squadmates, and not with the species you've allied to you cause
literally left with two trucks with missiles killing the one reaper left in our way
fuck this ending