Most harems are obviously ridiculous in that a very plain protagonist finds himself a harem of desirable bachelors, who, on top of all that are also virgins and despite all of this, the harem protagonist still remains a virgin and does not even kiss, as this would ruin it for the self-inserters, or something.
This title does away with all of that. The protagonist is very good looking; most of the harem members are certainly not virgins but quite perverted and unwell and it makes sense within their personality to either fall in love with him or at least desire him sexually. Furthermore, the title is interwoven with a dense plot explained by flashback that further influence the current plot until in the final arc the reason for the protagonist's being kidnapped is finally revealed and everything fits together.
It is obviously torture porn and an ode to masochists with most of the sexual content in some way being around torture, but the title continues to keep it fresh and introduce new forms of torture the protagonist, and other characters, have to suffer through.
With regards to who, if anyone, wins the harem.
It takes a most refreshing approach in that the winner is actually introduced half-way through the plot, and at the end kills the original “main girl" in defence of the protagonist to finally claim the prize. — This might be the only harem where the winner actually kills the original “main girl” after a complex plot at the end of what, is, perhaps, a bit too ridiculous of a gambit roulette on both sides after many switching sides and intricacies.