Among the 1000+ Hentai manga I've accounted for, to give one, I'd have to say
Select A Bride by Ryoma.
Art 9.5 / 10 | The art itself is outstanding, the illustrations of the sex scene are nearly perfect, not to rough, not too soft.
Libido 8.6 / 10 | For me to get stimulated it took about a few moments after entering the early sex scenes.
Organization 8 / 10 | The organization of the scenes could have been better, more foreplay before jumping to the sex scenes.
Originality 6.5 / 10 | I can't say this is the most original work I've read, there's a lot of doujins that are focused about the main character on acquiring some spontaneous wealth from some heir.
Characters 8.9 / The characters were pretty good, including the heroines, their characteristics is great and appearance, plus the anatomy is quite acceptable.
Overall 8.3 / 10 | Even not evaluating he manga, it's still pretty great, though it could have been better, a great read especially for all perverts alike.