I have a few things to say about this, but the first is fandom-specific rather than episode-specific, and that is, what the hell,
torch_wood? So much of the reactions post was just such a goddamned downer. This is a Doctor Who season finale, people, not a Torchwood filler. Which basically means that you can be a Jack/Ianto fanpuppy all you want, but that's a TW thing; just because you get to see it all the time in TW, that doesn't mean you have any reason to expect it from DW. So Ianto got overlooked. This is me caring. And I do like him! But frankly, DW will focus on DW characters, not TW-only characters.
Anyway, that aside...
1. The Regeneration. Interesting concept, but I think it was sprung much too quickly. I get that this was necessary for maintaining suspense, but I just feel like we were rushed through it entirely without getting much of a chance to pause and go, "Bwuh?" Also, points for unexpected naked!Doctor. Jack has already had his moments of nakedness, so I was both surprised and amused that the Doctor had his own opportunity for this. :p
2. Doctor!Donna. YES. Absolutely brilliant; I just loved this. Donna kicking Dalek ass and being all :D about it just made my day. However... the way the episode ended filled me with absolute RAGE. And as much as I can understand why the Doctor chose life without memories over a hero's death--because that's just the type of person he has developed into, and we have seen these kinds of decisions from him before--it just made my heart break to see Donna reduced to her former self. I say "reduced to her former self" because that's what I believe the Doctor thought he was doing, but from where I'm standing, he killed who she had become. Admittedly, I did not much care for Donna when she was first introduced, but she had gradually grown on me. Her final words--"I can't go back... Don't make me go back. Doctor, please, please, don't make me go back!"--are haunting, because they are the plea of a woman begging for one kind of death over another, and the Doctor failed to answer her final request, and all because he cared so much for her. Was that selfishness? Or was it a cruel kindness? Maybe it was both. But it was heart-wrenching all the same.
3. Three Doctors. Fucking awesome. That is all that needs to be said. Also, I want to see fanfic for this, and I don't even care if it's along the same train of thought as Jack's dirty dirty mind.
4. Ten/Rose.This was the biggest WTFery moment for me, largely because I adored their chemistry in the first two seasons. But this was just... awkward and painful. Shoving Human!Doctor off on Rose just fell very short of the mark for me. It seemed like little more than an attempt to appease the rabid Ten/Rose shippers and tie up loose ends. Very "blah" for me.
5. Jack's immortality and Rose's obliviousness. I was extremely disappointed that this was not cleared up at all. I just really wanted Rose to know that she was the reason behind Jack's I-can't-fucking-die syndrome, but now I'm pretty sure that will never happen. I just wanted to know her reaction: whether she would feel guilty, or proud, or just completely awkward - I didn't care what it was, as long as she finally knew. But no. Oh well, can't always get what you want.
6. Tosh saving the day post-mortem. While very deus ex machina, I'm glad that Tosh got a role in which she was able to save her teammates. However, I still want to know if Jack was aware of Tosh's project. I really, really want to believe that he was, otherwise... well, I don't want to think about otherwise. So yes, I'm really hoping that Ianto confronts Jack about that in the near future, though I expect that Gwen will more likely be the one to do so. As long as it gets addressed, I will be able to stop mentally gnashing my teeth over it. Really, Jack just can't be that stupid. Utterly reckless, but not stupid, and not about to walk out on his team again--not after showing how very much he cares about both Ianto and Gwen. I just want some resolution to this.