I've grown to like Capaldi as one of the best doctors (although I also agree that he's got some terribly uneven seasons), so it will be a shame to see him go, but his tenure has been deceptively long and it is about time for a change.
So long as the writing is there, the Doctor could be a piece of toast and it would probably still work somehow.
There is no shame in not knowing; the shame lies in not finding out