The characters are archetypes, the writing is lousy and full of stupid tropes, and there's usually unavoidable rape.
Oh yeah, I forgot to mention that I'm looking for games that do a good job of having gradual pacing, with the ability for steady forward progress while not allowing the player to corrupt the girl too easily.
The Fixer is a game I really loved when I was going through a female-MC phase, but it's a terrible example of what I'm looking for here. The game handles events with weighted randoms, so how slutty the MC already is and how much she's already done increases the likelihood that she'll do something a little more slutty. I like that in theory (it can make for a more titillating experience than just "unlock this scene when corruption reaches 20"), but only if it's balanced well. In that game, you gotta get lucky with the RNG repeatedly before she'll give up her virginity, and even then, it's easier just to get raped. Or, you can make the right choices in the prologue to have sex with the tutorial guy, in which case it's a lot easier to make other sexy stuff happen, but doesn't feel like corruption.
Anyway, that's just kind of a what-not-to-do example. I'd like a game where there's steady, but not instant, forward progress. Witch Trainer is the classic example of that, but I've played that repeatedly, and right now I'm wondering what the world of Japanese sex games has to offer the genre.