I remember someone posting a play-through of what I think was Rance 2
earlier in a Rance-discussion. From what I could tell from the play-through, the whole story and gameplay for that one was all about raping and sometimes having consensual sex with girls along the way (although, there were some scenes that were merely Ecchi, I suppose).
The main plot, to note, was that three magical rings had been taken by three girls and turned them evil. The only way of retrieving said rings was to defeat the girls in battle and then rape them to relieve them of their virginity, as the evil powers only worked on virgins. Some of the sex-scenes were optional, if I understood the LPer correctly, but others were mandatory events to progress the game.
While good gameplay and well-done plot may be a good reason to keep an Eroge*
VN, I feel that becomes moot in the face of the plot being centred around porn and rape in particular. I'm hesitant to judge a whole series based on just the knowledge I have of the series, but I think the content in some warrants a closer look into this series.