Personally, a game with romantic subplots isn’t a selling point for me. However, I do find the presence of romantic subplots or romantic subtext to be fascinating in games. I think you can break down many of these romantic subplots into a couple of categories. One would be “sexy” games which are frequently a JRPG and a dating sim combined. Another would be games with canon pairings. A final would be games with romantic subtext.
A “sexy” game is one where you tend to have a harem of girls that you can date, and the game tends to be packed with innuendo. A good example of this is Ar Tonelico. This game plays around with some of the common elements in a dating game, and is advertised in ways that focus on the sexualized aspects of the game. In the first game in the series, the plot specifically plays around with conventions. For example, a common dating game plot is a man entering a room to find a girl wearing only a towel. In the case of Ar Tonelico, a girl in a towel handcuffs the main character to a bed and says that she has to imprison him to keep him in her life. The scene may have “sexy” imagery, but it’s intended (and is) creepy in the game. At another point in the game, a cutscene involves a crystal being inserted into a female character with dialogue that makes the metaphor obvious.