If you're expecting major plot developments, there aren't any, this is yet another "slice of life" Yamayurikai. This season focuses on the development of Yumi as a mature and complex character, and not the goofy foil to her aloof big sister Sachiko. The usual suspcets are back, with more emphasis on the maturation of the younger sisters Yumi, Noriko and Yoshino.
Similar plot elements of dates, subtle yuri elements, friendship, family, and whatnot are back. If you haven't watched the other three seasons, you'll be lost in the various characters and their backstories.
This show, though, essentially is about the interplay between Touko and Yumi set along the course of the school year through different pespectives. It's slow, deliberate, well-paced and doesn't misstep too much.
With that said, the show almost indulges itself in its sexual ambiguity. It constantly teases and hints at relationships, only to pull back and make the characters just friends--which is somewhat unreasonable given the feelings it seems to portray they have for one another, something that makes it seem shallow. Or, another theory, is that the characters are good at smugly downplaying what happens behind closed doors, but that's hardly plausible in this sugary world.
It also abandons several plot arcs abruptly and just writes characters out from the final few episodes, which makes you wonder why they didn't streamline it from the beginning, making it feel a bit sloppy. Also everyone being sweet and kind, and only evil for a good reason is a bit cliched and you wonder if there are no bad people in the world of Maria Sama and all can be fixed with some tea and cookies.
