I miss Rhys Ifans as Mycroft
He was an absolute delight in the role, and that sinful voice of his... Goodness! I really liked how he and Sherlock played off each other, they really did seem like bickering brothers. His final two eps, where both he and Sherlock are attempting to rescue Joan and Sherlock is an absolute emotional mess still remains my favorite episodes of the whole series.
I do so hope we'll get to see him again, at least once more, before the series inevitably ends.