Having sex and/or nudity in video games has been around for... as long as video games have been, and it's always been controversial. Sex sells, period. And when you're looking at a demographic like, say, young teen boys (and girls), they tend to flock towards nudity and sex like moths to a flame. The 80's video games on this list are the best of the sexy games available for the system.In America and Europe it's still rare for gameplay to actually feature sex-acts or nudity as part of the game or something you can manipulate, but in Japan it's an entire sub-genre Eroge (erotic game).
After the erotic gaming Industry began in the 80's it didn't really evolve too much until the 90's with the advent of the CD-Rom, allowing not only better graphics but also FAR more room to actually tell a story. Games beyond just puzzle and card games were now able to be much more complicated and advanced and the Eroge genre thrived.