Has there been too much of the Master lately? Big Finish, BBC Books and others have out out a hell of a lot lately, and the fans have too (hey, I've contributed to some of it). Missy's appearance on the TV series seems to have kicked off a fan obsession with the character, with the various iterations and regenerations appearing more often than ever before, with multiple multi-Master events as well. It could easily see the character becoming overused to the point of sickness, but for now, I'm enjoying the extra adventures for the character. (We've even got Eric Roberts back, although I'm way behind on the various releases.)
Of all the incarnations, it's Missy who's the easiest to imagine having her own adventures, as a sort of wicked pseudo-Doctor. I've not picked up the first boxed set from BF, but the second one was recommended to me as having some irresistible ideas. This is true, but the execution isn't quite there.