Doomsday cleverly tied up a number of loose ends, while leaving enough dangling for future imagination. Obviously, at least one Dalek was not sucked into the void. The consensus seems to be that the Cybermen upgraded in this Universe had Cyber-suits that had been transported across the void and were therefore eliminated (this would tie in with the "emergency upgrade programme"), but you never know. Rose was the spoilt child who wouldn't accept that it had all worked out rather well for her; particularly after Father's Day and Rise of the Cybermen, she would choose the Universe with the Doctor rather than the one with Pete Tyler (never mind Jackie)?
Some other questions:
- It's not clear, but it seems to me from the Doctor's comments in Rise of the Cybermen that there is no Doctor in the parallel Universe; yet we know that there is a parallel Torchwood Institute. So who was responsible for setting up that?
- Presumably there are no Daleks in the parallel Universe either. Is this a consequence of the Time War? Or am I just banging my head against the plausibility threshold that there are some convenient coincidences about what is parallel and what isn't?
- In "our" world, Rose is dead. Do we really think Sarah Jane Smith isn't going to go investigating that? (I still have visions of her and Tegan Jovanka running a LINDA-esque self-help group - obviously without ELO or the tambourines, though)
- And where was the Face of Boe?
I can't say that I was inspired by the cliff-hanger, but Christmas specials are not necessarily representative of a series as a whole, and we know that Catherine Tate is not, in fact, the next companion.
Rating the season as a whole, then:
School Reunion (weak plot, but yay, Sarah Jane Smith!); The Girl in the Fireplace
The Impossible Planet; The Satan Pit; Army of Ghosts; Doomsday
Tooth and Claw; The Idiot's Lantern
New Earth; Rise of the Cybermen; The Age of Steel; Love and Monsters; Fear Her
No real turkeys on the Aliens of London scale, but New Earth was a weak opening story, and Rise of the Cybermen/The Age of Steel was a bit of a disappointment, even allowing for its place in the story arc. I do hope we can rest the Daleks for a while; RTD has managed to make them work again, but you don't want to over-use things and become formulaic.