I've never purchased an adult game on steam, but I leave them on because it's quite funny sometimes to stumble across them in my discovery queue. Lots of them have excellent reviews. Not as in they always leave glowing reviews. But they leave gooner reviews that make me chuckle. From the games I've seen advertised, I'm not sure what sort of sexual content would get a game delisted from Steam. Some are "artsy" projects, but many are straight up porn simulators.