It's good because it's a genuine, serious, well executed attempt at a very trashy concept.
Notice the absence of the ecchi or smut tags, and how little fanservice there is overall. It's there sure, but for the concept it's shockingly tame. A genuinely trashy manga would have spent the first chapter throwing at least 3 girls in very skimpy outfits on the OP main characters dick for no reason, then proceeded to introduce a new girl every few chapters, with heaping shitloads of fanservice to make people bother.
This manga spends the first 10 chapters elaborately setting up and justifying how OP their main character is and the roots of his bizarre and shocking motivation. he then doesn't actually get his first harem member until much later and she had to be won over by the protagonist solving basically every problem in her life while being a decent dude apart from the harem thing and EVEN THEN it wasn't enough until a heroic sacrifice he had no plans on coming back from made her realize just how much she would miss him.
And EVEN THEN she is still openly opposed to the MC's dream of a harem.