So I wonder how they're going to find him an extra 12 lives, I suspect something to do with going back into his own timestream he'll somehow come out before the 1st doctor and get all his lives back.
River gave him all her regenerations in Let's Kill Hitler. We have no idea how many he has left. Let's Kill Hitler was a terrible
episode, but that was a very smart move by Moffat, as it allowed future producers to avoid that issue unless they wanted to directly deal with it. A very nice move, unlike Davies refusing to un-fuck the Daleks before he left, so Moffat / Gatiss had to blow Victory of the Daleks in order to re-establish that they were Out There, Doing Bad Things.
One of my favorite Tennant moments is from "The End of Time" when he talks to Wilf about the bad things he's done and how regeneration feels like dying. He basically breaks down. It was very well done.
Right. Another example is in The Sound of Drums, when the Doctor talks about Gallifrey, and how Time Lord children eventually have to look into the Time Vortex, and some go mad, some run, etc. And then Jack asks him what he did, and the Doctor's all, "Pfft, I said fuck that noise
." When Tennant was allowed to be contemplative instead of an exaggerated caricature, he killed it. Most of the time, though, the scripts / direction just didn't allow for it.