It was worse than that; what you did during the game made no difference. The ending was determined in the last few minutes of play AND the 'best' ending could only be obtained if you played the multi-player portion of the game. The whole thing was stupid. I admit the game was rather enjoyable until the last 15 minutes or so but I also felt the ending and the method of determing which ending was utter crap.
This is not true.
You don't have to play MP part at all to get the best possible outcome (where everyone lives except maybe EDI, but since machines get "fixed" eventually probably she does survive as well).
To get the "best ending" without multiplayer part is possible, but only if you've used your own ME1/ME2 paragon savegames and bought every possible DLC with cutout story/NPCs. Paragon yes. If you do just two things as renegade, say goodbye to the "best ending" (Sheppard still might survive, but Anderson will still die).
The original ending is not an utter crap really, I've mentioned already it's Evangelion (certain old anime experiment with still ongoing debate if it is an unique masterpiece or worthless junk) rip off.
The problem is that the rest of the trilogy is not in Evangelion style and such ending is not "compatible" here. I've got so called enhanced ending a week ago in my replay and it doesn't completely feel like being kicked into a world completely different from the trilogy, still the whole thing wasn't really fixed. The AI with "illogical logic" star child and useless stargazer crap are still in there.
And it's not the moment you're about to enter the Citadel where things go down in ME3.
The moment where the game loses it's course and appeal is when Citadel becomes a spaceship and gets moved billions lightyears away above London for no real reason and without real explanation why since war is ongoing on Earth. What could Reapers possibly gain with Citadel there, if they needed to keep it safe, why not hiding it above already "done with" world?
And how was moving the Citadel even possible is something I won't bother googling or asking for an explanation.
All in all the ME trilogy ending was a fail whatever angle you take. If they wanted an earthcentric galaxy, they could have started with it, not ending with it. And should have put the game title as Earth Effect. Or London Effect. Or something.
Hopefully Dragon Age ending(s) won't be designed as disappointing.