They each have their own distinctive personality. If you think their personalities lack dept, remember that we are looking at a total of approximately 40 minutes screen time. With that in mind, I think the characters are well fleshed out considering the timeframe. We also get a satisfying conclusion to the plot despite the short time.
This next segment is not about "Mangirl!" in particular, but more a little rant on a lot of people's attitudes regarding miniseries.
I also think that this show (and a lot of miniseries in general) deserves a higher score than what it currently has on MAL. This is not just about this particular show, but short animes (each episode being 2-5 minutes long) in general. From what I see, it looks like a lot of people give short animes a lower score just for being short animes instead of scoring the show for what it actually delivers in terms of genre and promises.
That would be like if I (who does not like pure FPS shooters) rated a FPS shooter alone on the fact that I just don´t like FPS shooters, instead of looking at the actual game´s execution and its´ delivery and being aware of what is being expected for that sort of game.
Short animes work well with the comedy genre, but not with horror and very serious stories. At least from what I´ve seen.
I hope people will be better at distinguishing their own personal taste when it comes to genres and length, or at least be more aware of them, when rating a show. The reason I hope this, is because I think it would be a shame if a low score would end up preventing someone from watching an otherwise good show.
Until then; I´ve started to mentally add 1-2 extra points to the score I see given to a short anime since I think that often reflect the anime quality more correctly
