I find this fascinating in concept. I always like it when people appropriate legends and creatures in new and ridiculous ways, so I see nothing wrong with a sitcom about a guy forced to share a house with a snake-person or a pile of sentient protean goo. I’m sure the storytellers of ancient Greece and general antiquity came up with things like this. They just didn’t write them down.
The problem with most of these monster-girl series is that they’re typical stories beneath the new paint. The leader of the whole movement is Monster Musume, a manga and anime about an average guy with various roommates from the monster realm: first a lamia who can’t keep her coils off him, then a juvenile harpy, then a noble centaur, and so on. It adheres to the same bland template as countless other risque comedies, as nearly all of the mythical beast-women want the protagonist in one way or another. That's why I gave up on the series. Well, that and I started feeling sorry for the lamia, who met the protagonist first and clearly liked him best.
Monster Musume doesn’t hesitate to overload on titillation, and rarely does it take its premise to imaginative heights. For example, we’re told that lamia are all female and thus require human males to breed (gosh, how convenient), even though many brands of fiction have male snake-men. What about Michael Swanwick’s The Dragons of Babel, where a male lamia is called a lamius? What about the G.I. Joe movie, which features a serpent-emperor voiced by Burgess Meredith? What about those Piers Anthony novels that a lot of people warned me against reading? I’m sure at least one of them has a male lamia.
There’s one section of the monster-girl trend that I actually enjoy, if only for selfish, nerdy reasons. It’s a manga called T-Rex na Kanojo, or My Girlfriend is a T-Rex.
It’s ostensibly a parody of the whole monster-girl thing, and it envisions a world where dinosaurs didn’t go extinct so much as they evolved over untold epochs to live and work alongside humans. Of course, this evolution means that dinosaur girls look human as far as their heads and torsos are concerned—everywhere else they have scales, claws, horns, or armor plating.