Spoilers:
The biggest upset to me, about the ending, was that none of the hopes and dreams of the crew amounted to anything. Tali wanted to go back to Rannoch and rebuild their homeworld, get out of exile, etc. Shepard wanted to finally retire after saving the galaxy one last time, etc. None of that happened. Even if the galaxy barely survived, that's the ending I would have liked. I got so invested in the character stories, cared about most of my crew, etc, and none of it meant a damn thing. Either way, I ended up dooming the galaxy. (Red ending, still blew up mass relays, screwing over the inter-connected council races, etc as was said before.)
That deviant art ending a couple posts up is exactly what I would have liked to see. It didn't have to be super happy, but I wanted a sense of actually winning. Beating the odds. Each of the endings right now, still feels like the Reapers won in the end. Synthesis isn't survival, it seemed more like giving up to me(green ending). Controlling the Reapers isn't really an ethical decision(blue ending), and nothing I would have done in Shepard's position (I can see why it's a choice though, I like that.) The red ending, what I chose, allowed me to kill off the Reapers, but it had side effects I didn't like.
Because of this, it makes me really like that ending on the deviant art page. With every fleet, and the combined power of every race, how is that not able to fight off the Reapers, even with heavy casualties? I'm inclined to believe the dream sequence theory. Too many impossibilities happened, so it was either a dream, or rushed like hell right at the climax of the game(terrible idea for any game company, Bioware is smarter than that...). (No helmet in space, Anderson beating you there even though he didn't charge with you and even said nobody made it to the beam, etc.) And don't even get me started on the Normandy crash landing after leaving the fight... so doubtful that your loyal crew would do that. They've gone to hell and back with Shepard, even gone on a mission they knew they had terrible chances. Hell, in my ME2 playthrough, Jack died instantly before we even got to the Collector Base. They know casualties are always a possibility, and fight anyway. They wouldn't leave. It has to be a nightmare of Shepard's.
Edit: Holy crap sorry haha, wrote a wall of text and forgot to do the tags. Mah bad. >.<