It like comparing Tom Baker's Doctor to Peter Davidson's. Both are wonderful but vastly different. Baker was much more whimsical, Davidson a lot most wistful. Tennet has the whimsy, Eccleston has the wistful.

Personally, I liked Eccleston's Doctor of the two.

And I disagree they dumbed down Rose. I think part of it is that in the first season, Rose was still pretty innocent, by the second season, she's lost her innocence and has lost the bravado of innocent. She's a lot more aware of how dangerous and scary the universe is.