Although this was an epic episode, Moffat loses points for saying River's identity would shock and surprise people. It was the revelation that practically everyone saw coming.
Everyone being online geeks who basically worked out ever possible reveleation. Most of the audience at home didn't see it coming.
I think everyone's getting the wrong end of the stick with this - the "revelation" isn't necessarily that River is Amy's daughter. Well, that's part of it obviously, but the lesser part. The greater revelation is
what River, not
who she is - part Time Lord. And that therefore new Time Lords can be created by being conceived within the Time Vortex.
Having rewatched it, I did think the Doctors 'army' pulling off a win would have been a lot more dramatic and effective if the stakes had been higher and they'd been facing a more powerful enemy.
The Doctor's army didn't really pull off a win though, did it, because the whole thing was one big misdirection. It was a series of misdirections actually, with each side pulling one over on the other over and over again - but Eye Patch Lady was the one who got the last laugh.
The bit I wondered about was why exactly River couldn't help out on this one, and why she just plopped herself down at the end of the episode seemingly just for the purpose of delivering the revelation.
Then I figured it out - she couldn't be there, presumably because of a Blinovitch situation. Like when Adult Rose touched Baby Rose, if adult River were ever to accidentally touch Baby Melody, it would screw up everything even worse than it was and bring down the Reapers (as someone mentioned upthread). So she daren't appear to the Doctor until after the baby was already stolen.
Although that doesn't take into account the fake baby - does Blinovitch still take effect if it's only a ganger?
Still, that does seem to imply that, either the Doctor never gets Melody back, or River can never be with the Doctor or Amy again, until Melody grows up into her, or at least until she regenerates in New York in 1963.
Still, having River just pop in to say, "Oh btw, here's the answer to the question you've already all been wondering about for the past three years," rather than having the Doctor figure it out for himself, is a bit of a narrative cheat.
Was that even the same River as at the beginning of the episode, timeline-wise? Or was Stevie-Wonder-River from a different point in her own timeline than Luke-I-Am-Your-Father-River?