Don't get me wrong, I like Tennant as an actor. They've taken his Doctor to some interesting places, but I've come to realise I don't have the connection to his version of the character that I have with Eccleston, which is a shame, because initially I loved Tennant right out of the box. I thought he was a fabulous new direction for the Doctor.
So what's changed?
Well, I can't be sure without rewatching all the Tennant stuff back as well, and at the moment I can't be bothered (surely that's telling of problems right there), but I think it's a matter of character. And story, but mostly character.
The Tennant Doctor has become a series of check-boxes that must be ticked in almost every story. Doctor babbles on amusingly (tick!), Doctor gets dark angry (tick!), Allons-y (or however you spell it - tick!), and so on. He's mostly a collection of mix and match parts than a whole being.
Whereas the Ninth Doctor was actually a character. The only major obvious check box was "Fantastic!" Oh there were mentions of the Time War and so on, but his character reacted to the situations he found himself in in different and sometimes surprising ways as he grew and healed. He reacted to what was happening to the story according to his mood and the situation.
He didn't have stock reactions that were there as a form fan service, and neither did he usually react in a way that felt forced on the character just to forward the story in particular directions.
It's started to feel (to me) as if the Tenth Doctor reacts to the story in the ways that will make sure the expected check boxes will be ticked. 'Oh, David should be shouty and arrogant here, because we haven't done that for a little while...' or 'Well, he has to babble, it's his thing...', 'oh I know, let's have him go mega-angsty yet again, 'cos that never gets old...'
Interestingly, Waters of Mars handles it quite well, to a point. By making him listen to the destruction of the people he admires one by one, and racheting up the angst, when he snaps and saves people who shouldn't be saved it works. Oh it ticks the Time Lord/God box, but in this instance they've pushed the situation so far they pretty much had to have him save people.
In some ways it may have been a hell of a lot more interesting if he hadn't.
But their whole Time Lord Triumphant isn't exactly a dull idea, and as a direction for the character it is genuinely dramatic and new. Until they bugger it up at the end with Cheshire Ood and the Doctor becoming a gibbering wreck.
Then of course we get the little snippet from The End of Time where he's back to the checking the happy-go-lucky babble box. I actually liked that scene a lot the couple of times I'd watched it, but since watching Eccleston's version of the character all I could think was how much cooler and more interesting it would have been if it had been played much more low key, as if he's putting on the pretense of who he was, but his heart just isn't in it. And it would follow nicely from the end of WoM.
It's kind of a shame. The Doctor that delighted me in his early stories isn't there any more, replaced by the shorthand cookie-cutter approach to actual character. I don't care any more, I just want him gone so we can try something new.
Such a shame. I'm sorry, I'm so sorry.