It's about an isekai hero who buys sex slaves, takes them to fight monsters in dungeons and ends up building a harem. Its episodes have censored and uncensored versions, with the former even bleeping out dialogue as well as hiding boobs, sex, fellatio, etc. (But non-explicitly. This isn't hentai.)
That said, it's a lot better than it could have been. If you can stomach the fact that slave-owning isekai have become anime's latest questionable fashion (after incest), then Michio treats his purchases far better than they could have expected from anyone else in this culture. We're told that they'd all consented in advance to sex with their owners (although that's questionable from a slave), while they're undoubtedly better off with Michio than they'd have been otherwise. He treats his first girl, Roxanne, as if she were his wife and they were newlyweds. He buys clothes, armour, food, a house and outrageous luxuries like soap. (That's not a common item in that world.) He puts his life in her hands and consults her on all important decisions. Roxanne is always very aware of their relative status, but they're partners.
Even the "harem" bit in the title is mostly a lie. Michio doesn't buy a second girl until ep.11 (of 12) and there's no full-blown harem filth until ep.12's end title sequence.
It's better-written than I'd expected. The Roxanne-Michio scenes aren't empty wank fantasy, instead having a surprising amount of reality. I enjoyed following their life together. (Well, except for the sex scenes. These are nice too, but sometimes a bit dull. I fast-forwarded through some of them.)
I liked the show's balance on other moral issues. Roxanne and Michio go killing every day, but that's not distasteful because the monsters in dungeons are usually things like trees, sheep, rabbits, etc. (Yes, killer rabbits. The red ones are most dangerous.) On the other hand, though, bounty-hunting is a legitimate adventurer activity and Michio will resort to it when he needs money. He puts a cloth over a sleeping man's face and slits his throat. He decapitates a naked woman. The show's aware of the unpleasant side of this kind of life, even if it doesn't usually go there.
Leaving aside the "harem" thing (which is why I wouldn't watch a Season 2 if it happened), the show's main problem is there's no baddie. The monsters and bandits are just cannon fodder. Is there even a plot? Michio and Roxanne are just living their lives, really. Nothing goes seriously wrong for them. It's twelve episodes of wish-fulfilment, albeit with a couple of mildly tricky situations.
Personally, I enjoyed its accurate portrayal of a game world. Thus, for instance, my main complaint was that Michio should have given Roxanne more monsters to kill, for level-boosting. I liked his investigation of this job/skill system, how one gains new abilities, etc. The rules are detailed and make sense. Michio's quite clever in acquiring new jobs and making his party stronger.
It's like watching someone play an RPG. Have you ever found it surprisingly easy just to sit and watch someone's computer game? Yes, like that. (Could I compare it with watching snooker on TV? I used to spend hours doing that.)
The show gets funnier when Serii joins the gang in ep.11. It's fine. The girls are all enthusiastic. I quite enjoyed this show.
...but, despite its strenuous efforts, it's still questionable. If the sex slave thing doesn't give you the willies, you're not thinking about it. Similarly, bandits are fair play for bounty hunters and you can kill them legally, but I was still alarmed by Michio using one for death experiments in ep.7. (He wants to gain mage qualifications, which means using a spell to defeat an opponent. The outcome's no different from impaling him on a sword and it nearly kills Michio too, but still. Ew.) Ultimately, this show is about a desperately creepy fetish and doing an impressive but imperfect job of salvaging it.
But if you want to watch animated boobs, you could do worse.