I think Capaldi is a great actor, he’s had (contrary to what at time feels like the negative popular opinion) some incredible episodes. Like, some really, really incredible episodes. And he’s most definitely a good Doctor.
… I think it’s the right time. For me (and my daughter, with whom I was discussing this topic only yesterday) his Doctor is not as satisfying to watch as (the incredible) Matt Smith. Or David Tennant, for that matter. As nervous as I am about Moffat jumping ship, a brand new writing team with a brand new Doctor will at the least shake things up and make for an interesting refresh.
Go on BBC, have the spine to give us a female Doctor, yeah?