I've finally watched series 2 and 3 of Doctor Who, and though I adore Nine I can't believe how fast Ten became my Doctor. Nine was sort of wacky and cute and over the top, and Ten had all of that but also this darkness and depth that I found really interesting. Rose broke my heart of course, but I have faith she'll come back somehow. To me Rose is the core of New Doctor Who and even when she isn't there she's still at the center of things. The Doctor's grief after losing her could be its' own character, it's so oppressive.
Also, I like the irony of David Tennant leaving the show pretty much at the same time I discover how amazing he is.