There was only one thing I didn't like about this episode - making a robot go like a rocket with a sonic screwdriver. Eh? Does not compute. But other than that I found the episode nicely free of annoying crap. People have said they didn't like the over the top music, David T's over the top acting, and Russell T Davies' over the top dialogue. My brother actually phoned me while I was watching it on i-Player and said 'You'll spot the bits of dialogue that Davies wrote. You know what I think about them.' This is a matter of taste: in gushing emotionality, the line between uninhibited excess and disgusting surfeit is not obvious. For me, the emotionality of this episode pushed up against the constraints of excess, and that is what I like, because it's uncool. I can understand that other people draw the line differently, and it's all about context: I don't think there is a formula for getting it right. Quite often Doctor Who fails for me, I feel crudely manipulated, but not this time for some reason.
Another type of complaint is that people did not like the Doctor flirting with evil, or at least with megalomania. Instead of feeling 'well it's hard to draw the line', in this case I feel quite sure that this is something I do like. Not to say my friends who disliked it are wrong, but just that I am coming from a different place. I found it exciting and liberating.
Most fantastic plots have a black hole of nonsense in them. For example for Batman the black hole is 'Why doesn't anyone realise he's Bruce Wayne?' for Star Trek it's the Prime Directive, and so on. It's crucial to the franchise, but it doesn't stand up to that much scrutiny. I think for Doctor Who the black hole is about the malleability of time and the limits of power: there isn't really a coherent plot position, but many plots hinge on the issue. IMHO the best way to cope with this is what they generally do -- imply there is an ineffable level of meaning to which the human race is not privy, and which happens to accord with whatever is required in any particular episode.
That means the whole weight of each plot rests on the viewers' faith in the Doctor's integrity. Event X can be changed while Event Y can't, we just have to trust him. And in turn - going outside the story - this rests on our faith that this is a BBC pre-watershed show suitable for kids. It's not The Wire. The Doctor's moral integrity is guaranteed by the premise of the show itself, just like Batman's anonymity.
However, expectations of children's entertainment and what is out of bounds are shifting, and this could weaken the franchise. The moral line feels very wobbly to me sometimes. So I thought this was a sensible effort to confront those bounds, and thereby actually refresh them slightly, ready for a relaunch into a new season and a new Doctor. And so here the Doctor isn't just straining at the limits of his own sanity and goodness, he's raging against the limits of the franchise itself. No, he's astonished that those limits are nowhere near as constraining as he thought.
Of course Davies is always reflecting on the franchise - for better or worse it's the main thing that strikes him about Doctor Who. At it's worst he's all 'Holy Shit, I'm producer of Doctor Who, now dance my pretties!' and at it's best he's all 'This belongs to all of us, and says something good about all of us'.
So, no surprises that as he reaches the end of his reign his dialogue reflects on these issues - the vertigo of constraints dropping away. kalypso_v pointed out it's still very transgressive to have a show for little kids being resolved by a major sympathetic character committing suicide. That is the power of the franchise.