TL;DR - It's comedy with ecchi gyarus, and not to be taken seriously. Recommend if you'd like that. (Time of writing is vol4 completed and ch 26 reached.)
Title: Black Gakkou ni Tsutomete Shimatta Sensei (A Teacher Who Worked at a Black School)
Plot: A teacher starts working at a new school, however, all the girls in the school seem to be gyarus. What's more, apparently he has a massive d*ck, and they want a piece of it. Despite all of their advances, since he values his pride as a "teachers shouldn't do lewd things to their students" kinda person, he works very hard to hold back.
Scenery: Mostly takes place in school, and there's gyarus. Gyarus everywhere; often showing lots of skin and lingerie. At the time of writing this (completed vol 4, but read to ch26), literally every girl shown that isn't in the background has been a gyaru. There's also a lot of slang constantly being used along with lots of sex talk.
Genre (major):
Comedy - Most of the jokes are about the girls lusting over MC's god slaying p*nis. It'll be like this almost every chapter. He'll also occasional launch a few girls. (Literally launch girls with it)
Genre (minor):
Drama - Most of the read is a joke, but there will occasional be some story that adds a bit of drama.
Thoughts: I'd like to stress that this manga should not be taken seriously. It is very unrealistic and one may upset himself if he tries to apply logic to the girls' behavior to their teacher, or to the teacher's Excalibur. I'd say this is purely intend to be something to be laughed at and to give fan service. Though this is largely the case at the start (vol 1), as it's been going on, the characters have been more fleshed out and given back stories. Not sure where it'll head, but by the start of vol 5, it seem to have been going from 100% comedy to 70% comedy and 30% drama.
Recommend: I recommend this if you like a farce of JK gyarus! Particularly a comedic lusty gyarus farce. This seems to be a gyaru's lover's dream manga (I think). You will frequently see them either nude (though censored) or in fancy lingerie. They also behave promiscuously, such as having a threesome in middle school, and having sex with teachers as they please.
I do not recommend this if you plan to take this manga seriously.