So first things first. If Dean dies in the season 3 finale (I mean really dies, not the "I'll kill him this week, bring him back next" death Sam got, I'm going to start killing people.
I know a lot of people like evil!Sam. Never been my thing, but I do like the YED's implication that the Sam Dean brought back isn't entirely Sam. Cus he did seem a bit, y'know, off... So wouldn't it be cool if Dean gets all paranoid about that and is ever alert for signs of evilness, even seeing them where there aren't any. But really he's fine.
Also, if he was a bit evil, that would be okay too...
Sam's powers... Since his visions were all related somehow to the demon of the other special children, now they are all dead (apart from the new kids the demon got to. the babies) will he still get visions? And if so, what about? And if not, assuming that he even still has powers since the demon died (which he damn well better!) what will they be? Because we know he's got telekinesis, even if he can't use it yet. And who knows how the powers work, maybe he could get all of them. I'd like to see some Andy style powers, because I'm so sad Andy died, and it would mean they'd have to mention him. And also Sam could use his new powers on Dean
And talking of Dean having visions, I say more visions for Dean! I loved the one he had in AHBL, even if it wasn't entirely real since Andy caused it. Dean being all freaked out and "Come on! I'm not some psychic!" was so awesome. More of that please! (like that's gonna happen...)
So, they have to make some mention of this thing where Mary knew the demon. Partly because I want to know what that was about, and partly because I want to see Dean's reaction. When he saw it, Sam was more concerned about the demon blood he drank as a kid, but he must have noticed that, surely. And when (if?) he tells Dean, wouldn't it be awesome if he already knew!? I remember someone (I forget who) saying something about how reluctant Dean was to visit their mother's grave, and what if that's why. Also, surely John would have taken them there at least once?
The whole Dean sells his soul thing is so full of interesting possibilities, but like I said, he so better not actually die. Sam's all "I'm gonna save you" but Dean hasn't mentioned the whole Sam drops dead if he tries to get out of it thing. But there was no mention of anything happening to Sam if Sam gets Dean out of it. So that'll have to be the way they go on that one, surely.
It looked to me at the end there like Dean was pretty much okay with what he'd done, since it meant Sam was alive (since Dean couldn't cope with being alone, so he decided to die and leave Sam alone instead) but there's no way he'll happily die if there's a way out. SO I think he's going to be all stoic and stuff, but when he's alone really scared. But maybe more for Sam being left behind than for himself, because after all, the last time Sam was alone, he got killed...
Also (but it's a given) Angst, angst and more angst!
I could seriously ramble on like this all night, but I have work in the morning, so sleep might be a good idea...