The show's not a complete write-off, but it's an exercise in masturbation and its only virtues are accidental. It's another isekai with a ridiculously overpowered protagonist who builds a party of similarly overpowered allies and can crush any enemy he meets without even breaking a sweat. Also, most of them are female and sleep in his bed. One of them's his slave (and the hero accepts her sexual advances in the light novel, although the anime's backpedalled away from this).
It's okay, though. I didn't hate it. The hero (Kelvin) is passable and I liked his allies, although I'd have been happier had they been in a show that did something with them. They'll typically get quite a good introduction, then fade into the background of Good-Natured, Bantering And Badass. We learn more about Efil's background in the finale, but that's not the same as a character journey.
Anyway, the premise. A boy from our world gets transported to a fantasy world and given game-breaking powers! However did you guess? What's different about this one is:
(a) he sacrificed all his memories for additional superpowers, so he can't remember his former life. He's clearly from Japan, yet he's called Kelvin. No idea why.
(b) his occupation is "Summoner", which is super-rare in this universe. This lets him recruit strong enemies into his party, so I think you can see how the series progression will go. He ends up with a goddess, a slime, an undead knight, a half-elf slave, a Demon Lord's daughter, an additional hero and a monster wolf. Even in the series finale, which is supposedly when the one-sided fights get real, Kelvin treats the strongest class of monster as a training exercise for one of his party. When he's fighting the ultimate baddie (i.e. another isekai protagonist!!), his allies just sit around watching him.
Drama: zero. Suspense: zero. The whole thing's a foregone conclusion. You're only watching this show for the twiddly bits around the edges. In fairness, though, I like all of his allies. They tend to have backstory that makes you care about them, even if the show doesn't take this anywhere. Also, Kelvin himself is a nice guy and a good employer, so the show's title is a mystery. ("Black" in that kind of context would normally suggest dark, evil, exploitative, etc. Is it because he wears a dark coat? Admittedly, he acts like a knob around ep.7, but the deliberate misunderstanding is resolved harmlessly and without bad feeling.)
The slavery needs discussion. It's normal in this show's society, with sex slavery strongly implied. Efil becomes disturbed and insecure when Kelvin buys her but doesn't rape her. One group of villains are slavers, which we're meant to take as proof that they're evil. All that I can accept as part of this fictional world... but Kelvin seems to accept slavery as part of the furniture. He only buys Efil. He doesn't release anyone else from bondage by paying the necessary money, even after becoming wealthy enough to buy a mansion. (Even if he hadn't wanted to increase his party and/or make Efil jealous, he could have bought dozens of slaves and then just given them their freedom.) He doesn't disrupt the slavers' business. He doesn't even remove Efil's slave collar, which she's still wearing at the end of the season.
Mostly, though, the show's okay. It only gets annoying from time to time, e.g. the harem ego-stroking of ep.4. Kelvin's a battle junkie, which gets tiresome fast but is at least an (indifferent) attempt at characterisation. I disapprove of this genre, which is drama-free comfort food that's all calories and no nutrition, but I can see the appeal. It's basically the same as comic book superheroes. Kelvin's adventures are nice. He does good. He has superpowers. There will always be people who like watching that kind of thing, even without the additional targeting of involuntarily celibate harem otaku. (This show's not too bad in that respect. Kelvin's never seen to lay a finger on the girls who climb into his bed and my best guess is that he has monogamous intentions towards the goddess Melfina.)
Would I watch a second season? Maybe, if I had nothing better to do. I like the cast. I certainly wouldn't expect the show to become worthwhile, though, and it's at the low end even of its genre of "wank power fantasy".