I love the sound of the TARDIS

Furthermore, I adore the direction they're taking the tenth Doctor. He's been through so much in his 900 years, and even more in the last three or four (all numbers/dates subject to interpretation- this IS a Time Lord).
**Spoilers**
I've just finished Series 3, and oh, Holy Hannah! I've gotta start with the new Master. Delicious! First of all, he has some of the same body language and thought processes as the Doctor, highlighting the fact that they're really just two sides of the same coin. The Doctor interferes because he's trying to help, and the Master interferes because he likes to meddle, and he wants to be in charge of everything. Unfortunately, the Master's newest regeneration is blatantly insane; he's a megalomaniac and a psychopath. Some of the previous regenerations were a bit crazy, but you got the sense that there was a plan. The new one just wants to rule everything, and doesn't care how he gets there. And the terrible things he does to the Doctor! Ohhh, and the way the Doctor sets it right! Gorgeous! But then the Doctor is left to deal with the fallout...
Well, you know, it was bad enough when he thought he was the only Time Lord left, but then to find out there is one other, and it's his ancient foe... How horrible and wonderful that would be! And he tries so hard to help him, to rehabilitate him, and the Master just doesn't care, doesn't want any help, doesn't even want to be around if he can't be in charge and on top of the world. Of course, if one Time Lord can hide in this way, surely others could too. For the Doctor's sake, I'm not willing to believe that there are no others anywhere. I mean, Time Lords! The whole of space/time to hide in, and the technological capacity to change their biological makeup or create a little box outside of time to hide millions of Daleks in! They're out there somewhere, in little pockets and hidey-holes, and the Doctor will find them, gather them, and rebuild his society. I'm sure of it.
The Doctor is making great strides forward anyway. Losing Rose was rough on him, but I think Martha is even more suited to be a Companion. She's sharp, quick on her feet both physically and mentally, and an excellent observer. She also challenges him more than Rose did. I do feel sorry for her that he's so busy thinking about Rose that he doesn't really see Martha for a long time, or realize her feelings for him for a lot longer. I really want him to acknowledge his own feelings more, though. He keeps so much bottled up, in order to appear strong and in control. But you can tell Martha is good for him because he's actually said the word "Gallifrey" to her, and described the place a little, neither of which he ever did with Rose. It's cheesy, but I think in some ways, Rose was an anchor, keeping him from losing himself in revenge or misery, and Martha is wings, helping him get out and explore the universe as he used to love to do.
Finally, one of my favorite parts: Captain Jack. Well, really, the whole suite of "alternative" sexualities that populate the show. (also, Jack is HOT, but that's a side issue) First there was Jack, back in the first series, who flirted with anything that was sentient and bipedal. Then he kissed Rose, and immediately the Ninth Doctor. Yum! (I have a friend who insists they were a trio, and I don't really disagree) Then, early this series, there was William Shakespeare, who flirted heavily with Martha. When the Doctor called him on it, he flirted with the Doctor, who actually somewhat responded. Then there were the old lesbians, who insisted that they were married, and clearly had that old-married-couple dynamic. And now Captain Jack has come back, but the Doctor is more impatient with his flirting ways, and less responsive. Granted, that's for complicated reasons, including the effects of Rose and the time vortex, and the fact that Jack reminds the Doctor that Rose is beyond reach, but when Martha says something about fancying the Doctor, who doesn't see her, Jack indicates that he's in the same position. I gotta say, I was really hoping Jack and the new Doctor would kiss, since that would be hella hot, and also I think good for the Doctor, but there were good story reasons why they didn't, and I'm ok with that. There were also crazy revelations about Jack and another character we've known since episode 2 or 3 (ie 9th Dr), but I'm not going to go into that yet.
I'm not sure this fits the "alternative" sexuality topic, and I'm sure it's less of a big deal in Britain, but this season had a lot of couples with a black man and a white woman. I'm not sure what to make of that, but it does intrigue me, since even now that can be a hot-button issue in the States, and no one on the show even seemed to notice, let alone care, which is cool
In summation, I'm incredibly glad it all comes back at Christmas, since I don't think I could wait til next summer for more of the gorgeous, wonderful 10th Doctor.