Roundscape is a particularly good game. It has all the sexy bits you'd expect, and more. The writing is fantastic, the story is compelling, and the characters are well-developed. HOWEVER I want to draw attention to a few things. First, it is a particularly good
game, so if you just want to click & fap you have better options. Second, the artwork is inconsistent. It's pretty much all good, however the styles change quite dramatically at points and that can put some people off. To me, it still looks like different takes on the same characters.
The story, however, is really something else. I won't spoil anything, but there was a particular part where I came across a demon and because of my starting class (Paladin) it so thoroughly bothered me that I spent the next 2 hours plowing through other storylines to complete this particular one. Seriously, the writing is good.
Overall I HIGHLY recommend it, but if you're just looking to beat off quickly then there are better options.
For example,
Dreams of Desire is a classic with multiple endings (sorta) that gets to the action much more quickly and has a harem storyline.
Sisterly Lust is another great one with a possible Harem ending.
Depraved Awakening is superbly made with some Harem aspects to it, but you need to make the correct decisions. Extraordinarily good renders and a powerful storyline.
Finally,
Long Live the Princess has not been completed yet, but it edges into some of the genres you mentioned. It's probably my favorite game in the genre and has one of the most disciplined devs in the industry.
