As a long time fan of Doctor Who, I'm struggling to get particularly enthusiastic about Series 9 based on what I've heard so far.
The Missy character never especially thrilled me, so having her back as a recurring villain is bad news (if nothing else, it spoils the one good moment in the Series 8 finale where CyberBrig casually blows her to pieces - which is both a nice throwback to his "Nice to be seeing you again [WALLOP]" in the Five Doctors and a rather poetic end to Sir Alistair's character arc). I always felt she would have been better as the Rani or as an independent character rather than the Master (and the "reveal" was little of the sort since it appeared that many fans had sussed out the Missy -> Mistress -> Master gimmick from the moment the Deep Breath scripts were leaked).
Overall, I just want to see Steven Moffat step down. As was mentioned earlier, Russell T Davies did four-and-a-bit series then moved on, whereas his successor has now done five series (plus the Golden Anniversary) and apparently has already bagged a sixth. There has developed a large segment of fandom who feel that his time has long passed.