The Ninth Doctor's catchphrase was "Fantastic!", but I think that the Tenth prefers to say variations of "That's brilliant!" I really like the Tenth Doctor; David Tennant is doing a brilliant job at portraying his character, and the writers have done a smashing job with the plot.
I just finished watching "The Impossible Planet" tonight (yes, I know the CBC is behind on the shows...). Wow. Part of the reason I love the Doctor, of course, is because he's one of the last action heroes on TV who is fun for the entire family. He doesn't swear and spit as he shoots a massive laser gun into the hordes of rampaging aliens. In fact, when the chips are down, he is usually seen admiring the work of his enemy and attaching adjectives like "brilliant" and "stupendous" to things.
Like in tonight's episode, the Doctor and Rose end up beyond the range of the TARDIS' knowledge--smack on a base on a planet that is orbiting a black hole (as opposed to being ripped apart by its gravity). And the Doctor, upon hearing the story of why this ship full of humans came to the planet, hugged the captain. He even warned him--"I'm going to hug you now." He hugged the captain because he just loves the human spirit of exploration. And watching the Doctor's admiration for adventure, especially when it comes to beating the odds, is quite enjoyable.
Of course now I can't wait until next week's episode to find out how Rose and the Doctor get out of this one... (no spoilers!!)