Starting to open up to it, but it's generally not my thing. I think it's going to depend on the relationship that the characters have. I lean more on the intimate relations rather than the trashy ones.
They usually use poorly compressed images and videos. and are poorly made because the platforms used are not well suited for this kind of gameplay IMO.
I am partial to those sandbox games like hentai highschool and Strive to Power/Conquest, Lilith's throne.
Also Night Games while not really a harem game comes pretty close.
I find that most of the time, the collectibles are not worth it. I prefer when the renders are in context of the story. Otherwise, it just feels random.