He had a good run but it's probably a good time for the change.
Agreed!
"My" first Doctor was Tom Baker. "My" Doctor, however, is Christopher Eccleston. Don't get me wrong. I love all my children, even the crazy ones (i.e. Colin). But, Chris did something that, really, only Tom Baker has done before, and that's created an entirely NEW persona, relatively free of previous incarnations. That's always been what keeps me from getting into Tennant as much as everyone else. I can literally see David using bits and pieces from previous Doctors to create Ten. And honestly, it just never comes across as sincere for me. The entire time I watch David Tennant, I'm fully aware that he's "playing The Doctor". Which, taken in small doses, is perfectly fine. But, I cannot readily describe Tennant's Doctor without using the same adjectives I would use to describe Tom Baker....."zany".
Eccleston, on the other hand, came in with a Doctor I had never seen before. He didn't remind me of any Doctor previous, and at first I was taken aback a little bit. But, as his season progressed, I begin to realize I was watching The Doctor....a lonely, ancient godling who was suffering from a post-War trauma, and a severe case of survivor's guilt. Culminating that into an obvious deathwish, and the 9th Doctor became something completely new to Doctor Who. Which is exactly what it needed.
I think Tennant did a great job, for a fan who landed the role. However, I hope Smith's relative detachment from being a fan of the show will prompt some more of the "new" that Christopher Eccleston brought to the role. He was, as you would guess, Fantastic!