After just watching "Silence in the Library/Forest of the Dead" for the first time, I have become puzzled.

When River connects herself to the computer and kills herself, the Doctor is devastated, very nearly crying. He is then exceptionally tempted to look in River's diary, only preventing himself on Donna's say-so, and he is then obviously delighted when he realises he can upload her Data Ghost to the virtual world created for CAL.

Fast forward to the Time of Angels, and the Doctor treats River almost like a nuiscance. He mocks her attempt to fly the TARDIS (You call that flying the TARDIS!!!), and attempts to leave her behind on the planet with the crashed Byzantium, clearly showing signs that he wishes he'd never picked up her message. He shouts at her several times, tells her to shut up, and treats her horribly right up until the end of the episode. Now, I understand that Ten and Eleven are vastly different, but surely, after being so devastated to see her die, the Doctor would show some sign of happiness to see River again, but he doesn't.

My question is, why? Is this to show the difference between
Ten and Eleven, or was the Doctor "being Doctor Grumpy" that day?

He has witnessed her die. Maybe he is trying to peev her off so she leaves him alone and doesn't die. Changing history. But that means he wouldn't be mean as he didn't see her die, so history would change. Blast! Ignore my theories!

They are two very different Doctors, and the tenth Doctor's sadness at River's death was only the same sadness he'd show at any death. He seemed to me less than pleased at being manipulated by someone who clearly knew him but who he didn't know, even then.

There's at least one (probably more) unseen meetings between the 10th Doctor and River (implied in the script and stated offscreen by SM) so their relationship has developed since her "death" in FotD.

In The Silence in the Library/Forests of the dead the Doctor met River for the first time, and was initially unsure of whether to trust her. By the time of her death he had learnt that he could trust her and that they were obviously going to share a close relationship in the future. He was devastated by her death partly because he was growing fond of her, partly he would be upset by any death, but partly because she sacrificed herself in his place, so saving his life.

In The Time of Angels the doctor meets River for the first time since he sees her die. Of course this is upsetting for him, especially as she is of course unaware that he has witnessed her death. He doesn't want her to know what he knows, so he wants to leave as soon as possible, but finds himself involved in the whole Byzantium thing against his better judgement. This makes him "grumpy".

As for the way he treats her, they treated each other like 2 people who knew each other very well and felt they could say anything to each other would treat each other. Banter, private jokes (handcuffs) grumpiness, a bit of resentment, affection were all there.

Amy picked up on this when she called River "Mrs Doctor".

One of the things that stood out for me in the Angel 2 parter and in The Pandorica Opens/The Big Bang was how River knows what the Doctor is thinking (e.g. realising the statues should have had 2 heads) and he knows she will get his meaning immediately. Either that or they think alike because they have been together so long River knows him inside out.

I really hope that River gets a good story in series 6.

True! It would have been a bit strange otherwise. If River had met the Tenth Doctor for the first time in the library, after countless run ins with the Eleventh, she'd have been bright enough to think "Hmm, this could be awkward" rather than go with utter confidence that this was just another Doctor who knew her and then get totally downtrodden when she found this wasn't the case.

I rewatched this one recently and it was incredible how Moffat wrote the early dialogue between them in such a way that she could go on for so long without realising that he didn't know her yet and he could go on not realising that she did know him. Really brilliant bit of writing.