Monster girl anime is a niche genre that's started to make its way into the mainstream. These shows feature girls and women who aren't exactly human - instead, they're centaurs, demons, dullahans, vampires, zombies, and all manner of mythological beasts.
More often than not, they're overtly suggestive, totally adorable, or some combination of the two. Monster girls in anime commonly befriend male humans. Soon enough, the man finds himself surrounded by a harem of them.
The genre has a lot of crossover with ecchi, harem, and other related genres, and it tends to include a lot of fan service - Monster Musume and Rosario + Vampire are well-known examples that follow this trend. There are also shows, including A Centaur's Worries and Interviews With Monster Girls, which use monster girls to explore social issues.
Whichever tone you prefer, if you like your anime with some fantasy sprinkled into it, you'll probably find something you enjoy in the monster girl genre.