
As for David Tennant, hard to tell. He was 'unconscious' for most of the Christmas episode, and when he came alive, he seemed to be aping some of Eccleston's goofiness/humor. Although I liked his more serious moment at the end with the Prime Minister.
I'll reserve judgement til he has a whole episode of his own.
My wife doesn't like him because she thinks he looks like a weasel

I'm looking forward to the new series. Yes, K-9 returns (in Episode 3) with Sarah Jane. I'm also looking forward to the return of the Cybermen, although I'm not really wowed by the new design. I always preferred the Cybermen to the Daleks for some reason. I wish they had been a little more adventurous with the Dalek design too.
As for less 'Earth' stories, I believe the scripts include more 'alien world' stories. Personally, I just want to get away from Earth for less Mickey and less of Rose's annoying mum.
Hehe, as an aside, whilst looking up info for this reply, I noticed this wallpaper and was amused.