Who should watch it?
Anyone who wants to relax with slowly paced story and silly jokes. Anyone who'd like to get back to high school, just to do crazy stuff with his friends. Anyone who has enough of magic, sci-fi, violence and romance in other anime.
Who shouldn't watch it?
Those who love action - there's very little. Those who are impatient - the show goes really slowly. Those who watched first episode and didn't like it at all - all eps are like that, so stop now, watch something else.
Now I'll deal with detailed review:
Story: (5/10)
Meh. Nearly none. But, because of randomness of the show, it's no issue. It's all about classmates, as they spend their time during high school education. The story covers 3 years, during which there's many things happening, but it cannot be considered enough for anything higher than 5/10.
Art: (7/10)
Not bad, although the creators love to use super-deformed forms, and the art isn't detailed. Nothing unusual, nothing original, but also nothing lame.
Sound: (8/10)
The opening and ending song are representing two main properties of this show - funniness and nostalgia, respectively. The voice actors do their job well. In the show, you can hear many catchy tunes. Nothing bad. (Yeah, I wrote some nonsense here, but I don't care about either art or sound. It's the story that matters.)
Characters: (9/10)
Well, after you see Osaka/Chiyo/Tomo/Sakaki, you'll have to agree. Each character is original, and many of them change during high school. It's all about the last period of the childhood and entering the adulthood. And about craziness and silliness, too.
Enjoyment: (9/10)
It was simply nice. Not as much funny as nice. It is one of those shows you watch totally relaxed, knowing there's nothing to destroy the happy atmosphere of the show.. It's just random craziness but in low speed. Pretty nice for the evenings, when you have no energy for following a fast paced story.
Overall: 9/10
