STORY
Oresama Teacher's pacing is sort of the worst thing about the manga. The general plot isn't bad, and is in fact a good hook--delinquent girl must hide her unscrupulous past while fighting to save a school from closure, all while making friends (tm). It's a bit generic, especially the friendship-gathering, but the facet of hiding Mafuyu's past delinquency is interesting.
But--and that is a huge but--the way the mangaka paces this manga is poor. I often find myself utterly confused as to what is happening and why. The manga is released monthly (more or less), and every month, I'll have forgotten what the past chapter covered, and will then read sixty pages of confusion. I've taken to writing a small summary of where the plot is, and reading it whenever a new chapter is released.
This happens for two reasons, I believe. First, the manga doesn't really recap what happened last time very well. It feels like they are simply drawing the next page, instead of opening the next chapter. Second, the plot itself can be, at times, unclear. Why are they doing that? What are they doing it for? I don't know! This is likely a two-part issue: an average translation, stacked on top of an already-vague narration.
ART
The art is standard fare for your average manga. In general, people are drawn well--nobody suffers from stupid-face. It's very representative of the style towards which many shoujo manga have moved in recent years. However, there are two major flaws which come from this industry-wide art shift.
First, many characters resemble each other greatly. There are very few women in this manga, and tons of guys. This is a problem, because the mangaka seems to have a limited set of eyes + hair + size to work with. The art is not greatly detailed, so the characters tend to blend together.
Second, backgrounds are often just gradients, or slapshod drawings of lockers or doors. It's not very detailed, basically. This isn't as big of an issue as the last problem; in the end, this is not a manga to write home about. It's one you read because you like reading manga; it's not trying for any prizes.
CHARACTERS
The characters are surprisingly interesting. There are few trope or stock characters that truly exist. There are plenty of delinquents, and while they appear standard, they often show depth of personality (or at the least interesting traits).
Mafuyu in particular is nice to see. For whatever reason, she's absurdly strong, but her personality is not shoehorned into the Strong Female Character trap. She's dense, and plain, and dorky, but in ways which are utterly normal. She's well written, and a great female action MC
ENJOYMENT/OVERALL
Despite the faults in plot pacing and art, this manga isn't half-bad a read. As said earlier, it's nothing to write home about, and it knows it. It's not trying for anything profound, or weaving a grand tale. It's like reruns of CSI or Seinfeld--it's something that you read when nothing else is happening, and you enjoy it, and then you are done with it. For that purpose, I'd recommend the manga.
