While teasing readers with yuri is a big part of the series (big surprise), I personally think that the series' strongest parts are the pretty solid humour, interactions between characters, and of course, the major theme of friendship. I would by no means claim myself well-versed in manga or literature in general, but this series might have one of my favourite overall casts in all of fiction.
Of course having over 150 chapters in a world where time doesn't pass would help you to show off multiple sides of your characters. I still really adore them.