She could be a seriously awesome and awesomely serious Doctor, given the chance. I've only seen snippets, but I believe she's quite the actress in her other stuff.... But we do not need more Tennant. He was never enough of a Doctor compared to other iterations and way too crazy-madcap, despite being entertaining in his own right. We need more Capaldi, with a good dose of Matt Smith's capacity to evoke previous Doctors while hinting at a really old being in a young body... we need someone who can seem like they're actually 900 years old.
Without that, the Doctor is little more than a Childrens' TV presenter.