Best 2 are Sengoku Rance (Rance 7 canon) and Kichikuou Rance (Rance 5 alternative route), definite 5 stars. I want to compare these 2 to Dieselmine's "The Salacious Story of Huayin" as its also a Japanese strategy rpg hentai games.
Art:
Anime-styled, much better looking than those dozen of Japanese RPGM games
Well proportioned characters, also range anywhere from children to average to super buffed dudes and bootylicious women.
"The Salacious Story of Huayin" has more hot/sexy/extreme art than Rance series.
Gameplay:
Kichikuou Rance 1996 and Sengoku Rance 2006 has similar strategy gameplay, that is you are presented a map, you control an area, multiple commanders and armies, your "initial goal" is to capture the whole map from many other warring factions.
Gameplay has a certain depth to it. You may expect a lot of mechanics to try out, but once you get a hang of it, most are just optional. So enjoy the game as your own pace, as its not hard and grindy, unless you play Rance 7's higher difficulties that only get unlocked after first playthrough.
Complex wise, both game has more and better gameplay than "The Salacious Story of Huayin". You can expect 10~40 hours gameplay for one Sengoku Rance playthrough, ~50 hours if you want to explore everything in Kichikuou Rance with a walkthrough. Walkthrough is definitely useful, but i suggest to not spoil yourself too much, as the story is interesting.
Obviously not as complex and stressing as playing the likes of Civilization and Total War. But the most complete gameplay experience ever existed in a game with large amount of sex.
Story/sex:
Protagonist Rance is an arrogant, narcissist, skilled swordman. He travel around the world with his slave Sill. In these 2 games he takes on the role of a leader of a region.
All characters has a consistent personality. There are no women who, prostitute herself out in one scene but get disgusted by seeing a dick in the next scene. You will likely feel love/hate toward certain characters
Good amount of sex is male dominance. Rance like to force women into sex, however he treat his women well, and try his best for his partner to feel good. You could say he is a rapist, well, remember that him being willing to risk his life multiple times to fuck any women is a joke in it's own, so dont take that too seriously. There is unavoidable rape not done by Rance in the game and thats way worse than what Rance do.
In short, definitely try Kichikuou Rance and Sengoku Rance out. I know many Japanese/anime styled games are just low budget trash, Rance series have a respected hitory of having existed since 1989, 30 years ago.
Play Kichikuou Rance first if youre patient, can tolerate the somewhat outdated art of a game from 1996 ( then again, still better than the shitty Japanese games nowadays). Or Sengoku Rance first if you want to jump right into the best game.
The other games of the series are not as interesting and worth your time, unless you are already hooked into the story of the series. I myself started with Rance 7, the best of the series. Rance 8 9 10 are not yet available in English, no idea about that. Buy the game from Mangagamer if you can, its worth it