Nobody expected The Doctor to die, so having him not die wasn't surprising.
Having the a large chunk of the episode be "An emergency in a messed up timestream" wasn't interesting, because said timestream didn't exist at the start of the episode, so we had no emotional investment in it.
Having it just be "It wasn't him" was a massive let down after having been told that it was him.
Basically we've been looking forward to finding out how The Doctor would avoid dying since The Impossible Astronaut, and after that amount of time having it just be "It was a body double" seemed like an awful way out, as we were reassured in that episode that it definitely was him.
So, 2/3 of the episode taken up with stuff we didn't care about, River Song telling us she'd rather have the universe be destroyed than the man she loved, and then a "Oh, it wasn't him after all" ending.
Not surprising that I'm disappointed.
I'm now assuming that Moffat's grand plot arc will carry us through to the 50th anniversary in 2013. And frankly, it already feels horribly stretched, by that point I have a horrible feeling I'll be beyond bored of it.
(I did like the scene with Amy and Madame Kovarian.)
Original post on Dreamwidth - there are comments there.