Tennant's Doctor is definitely a different man. He doesn't go to the dark place so much as the lonely place. Where Eccleston's Doctor was all bright whites and shadowy blacks, Tennant's is more fickle yellows and gloomy blues. I find Tennant's Doctor less dark, but more lonely. I find his Doctor seems older, somehow (which sounds ridiculous, I know). Where Eccleston's eyes were magnificent at translating the dark place, Tennant's are good at reminding you it's been a long, lonely life for this space-man.

Glad you enjoyed it, though! I'm a recent convert myself.