I'm not as disappointed as a lot of you seem to be, but neither am I particularly impressed. I spent quite a bit of time deliberating over which option to choose (long enough for me to actually die, with a message saying that the Citadel had been destroyed), but from looking at the other options available it doesn't seem like it was worth the concern. Went with Synthesis, but was a hair's breath away from choosing Control. No effin' way I was going to destroy all the Geth after how much help I'd given them over two games.
Just needless questions raised by the ending though. Like, I had Tali in my squad on Earth charging towards the Crucible (as my love interest) - why was she suddenly on the Normandy when it crashed on the new planet? Was there any way any of my squad were actually going to die like in ME2? Is that even possible?
And probably the biggest point of contention, and I swear to God this isn't just me flashing my obligatory fanboy card or anything, is that all three endings are pretty much exact copies of the choices from Deus Ex! Destroy all synthetics (Destroy all technology/Dark Ages ending), Control synthetics (Rule tech with Bob Page), or Synthesis (Merge with Helios). It's not even subtle! I mean, if they were ever going to rip a game off they chose the right one to steal from, but still...