Landmarks No.46

The End of Time Parts 1 & 2.
The end of the Tenth Doctor.
The return of the Master, and of the Time Lords.
The last appearance of the "Children of Time" and some other Tennant characters.
Our only glimpse (to date) into the Time War.
The RTD era comes to a close.
Matt Smith makes his first appearance - ushering in the Moffat era.
David Tennant had the option of staying on for a further season under Steven Moffat, but chose to bow out with Russell. Before he leaves us, he gets to have a tour of some of his old companions - including seeing Rose before she had first met his Ninth incarnation. Martha has left UNIT and married Mickey, and they have set themselves up as a freelance alien fighting outfit. Donna finally makes it up the aisle. There's closure of sorts for his relationship with Joan Redfern, as her descendant publishes her book. Captain  Jack gets set up on a date with Midshipman Frame.
Wilf becomes the full companion for this story - and proves to be the one who will knock four times.
Tragically, this marks Lis Sladen's final appearance in Doctor Who.
Rassilon and the Time Lords appear, in a ruined Capitol littered with crashed Dalek saucers. The War has corrupted them completely, so it is not a joyous occasion for the Doctor to see Gallifrey live again.
As a story it is a bit bonkers. Instead of enslaving everyone on Earth, the Master becomes all of them. The manner of his resurrection is, quite frankly, stupid. His madness is fully explained at last.
When last seen, the Master is dragged back into the Time War with the rest of Gallifrey. Have we seen the last of him? I very much doubt it.
Sadly, Moffat will throw the baby out with the bathwater, seemingly determined not to use any of the RTD characters - even Jack. He'll make changes across the board - some successful, others less so.