Have watched all three- enjoyed them all, so post 7900 dedicated to 'So Long'
A)I like 'time slip' dramas, a common Japanese drama plot device, but this one using the cassette tapes worked nicely. Mayu & Mariko very strong in their roles, although putting a long haired wig on Mariko to establish 'high school aged Mariko' was not quite convincing. And bonus points for having Ren Osugi in a supporting role- really added that extra touch that made this drama as strong as any you would normally see ,as opposed to 'idol drama' - (e.g. Morning Cop ~Daite Hold on Me!~) Ren Osugi also appeared in the new Wonda Coffee CM with Mayu.
K) I haven't watched Yuko's past dramas, but I knew she was a good actress, so I had no problems with her playing the reserved role. Walking out on the stage barefooted, and playing 'Twinkle, twinkle, liittle star' was indicative that the Yuko Oshima DNA was alive and well....Jurina was a pleasant surprise. As soon as her 'Juri Ueno' type character was revealed, both carefree, and annoying, I knew there would be a dark secret, and Jurina handled the part with good skill. And again, a common plot driver in Japanese dramas (and other countries) is the 'misunderstanding' that usually takes all season to clear up. But as this is a one time drama, the misunderstanding could not be fully exploited. I did enjoy Tomochin, Mochhi, and KitaRie, in their quick roles, almost thought a fist fight was gonna break out. But as the story progresses.....well, bring your handkerchief.....
B) Unlike the first two, as everyone has mentioned, this one spread the lines around to much more of the team. I think with three dramas, it was not a bad idea to have one of them be more of an ensemble piece.
Team K was fun because so many members had cameo roles (such as the clerks at the store where Yuko was buying her work suit), but team B actually gave lines to a lot more members. And I think it nice that Mina Oba gets a small role, but one that is a plot driver, as her interaction with Milky was important. Or Rena Kato, girl may be newer to drama, but she has Academy Award worthy gigantic tear drops that spice up any sad scene. And I think the plot had something very positive to say- of course losing a teacher who is still really young is extremely sad, but from this tragic circumstance, Paruru and the Gish overcome their guilt and hatred, a positive life change (similar to Milky making a change after running into Mina Oba).
So overall, I though the quality of all three dramas was pretty good, and plots, although not groundbreaking, were interesting.
And a high school that employs Haruna Kojima, Ayaka Umeda, and Yuki Kashiwagi as teachers must be doing something right.