I have a complicated past with this series. I ended up watching every season even though I just started watching it because some people were complaining about another show stealing a very well-known sequence from Maria-sama ga Miteru.
Right now, this is my favorite TV show. However, I didn't particularly enjoy it at the time; I watched it all very quickly, and I don't think that's how this series was intended to be viewed. I made a lot of mistakes the first time, which led to the impression that the characters were observing other people inanely. For example, it's simple to binge-watch those slice-of-life school comedies if you're only looking for a few laughs, but Maria-sama ga Miteru offers rich interpersonal relationships, believable characters, and a character development that makes it worthwhile to take your time.
Overall, the seiyuu are excellent and do a great job of expressing the emotions and ideas of the characters. The animation, on the other hand, could have been better; some scenes appear a little artificial or even mechanical, but generally, I don't believe it takes away much from the series, and I liked the artwork.
Unlike most f/f shows, this one is intriguing and unique. For lovers of melodramatic minor character lesbians, this is a must-watch because of the delicious subtextual f/f and canon content.
However, I think that even for people who aren't very into f/f or don't like it, Maria-sama ga Miteru would be entertaining. If the excellent characterisation is what you're looking for in anime, then that should be enough to lure you in. To put it another way, if you're inclined to view it that way, this series doesn't necessary focus on f/f too much. That's the allure of subtext.
Oh, and in case it counts, the setting-a private Catholic all-girls school-and the series name don't center on religion. It essentially just revolves around a bunch of young ladies and the relationships that develop between them, which I suppose puts it squarely in the shoujo genre.
Therefore, Maria-sama ga Miteru is not suggested for people who just like to see two females in ridiculous, compromising scenarios or for those who just like panty shots. (Please watch the seinen series for that fanservice content; this does not contain any fanservice.) Those who enjoy a lot of action should not watch this, in my opinion, as there isn't much of it. This is also not for you if you need a grand narrative to keep your interest because it's slice-of-life with a strong dramatic undertone. This is for fans who have been waiting impatiently for a series with, at last, compelling characters.
