As someone who has seen his share of Rule 34 on the internet, a common fetish is Cute Monster Girls, and the cliche is that a world of monster girls would involve a lot of rape of unwilling men, but willing guys would enjoy the hell out of it. It also paints the world is slight crappy as a result, but bearable if you don't mind having sex with monster women.
This game takes the concept of the Monster Girl Encyclopedia, turns it into a visual novel with RPG elements, and basically sets about exploring how this concept would actually work out, even deconstructing the cliches and lampshading the rest quite a bit.
Below is my take on various aspects of the game.
Gameplay: It's a visual novel that is largely guiding you on rails, the only choices being during battles and some story scenes, as well as a few villages along the way, but the meat and bread of the game are the battle scenes, which involve a lot of choices, a fair bit of luck, and a love affair with the save/reload options.
If that doesn't annoy you, it does the job well enough.
Art: The art in this game is slightly rough early on, but gets better over time, both the hentai and non hentai stuff alike. Some of the monster designs are actually quite well detailed, with some of the ones in the third part of the game being Lovecraftian nightmares with impressive detail. Backgrounds are a little shoddy in places, but otherwise look decent enough. It does have inconsistent art, as multiple artists contributed work to the game, but this also gets better with time, though the main character art is all over the place proportion wise in a lot of battle/scenes.
Sound: Most of the soundtrack is Public Domain classical music, though the original music is good enough, with some of the later music being excellent. Sounds effects and voice clips are passable to above average, most of the time.
Story: This is where the game shines. It starts off cliche as hell, but immediately starts picking apart those cliches very early on, and by the end of the game, a very black and white world is shown for all of it's intricate shades of grey, and while I don't want to spoil too much of the plot for anyone, let's just say even if you don't like the hentai scenes (I wasn't the biggest fan of many of them, and some are downright nauseating to watch to be honest since voraphilia is not my thing at all), the actual non hentai plot is pretty damned good, about on par with Shin Megami Tensei series in some ways, even offering a choice between the game equivalent of Law/Chaos at one point, though by end it should be obvious what side is the winner, but even then no one, not even the Big Bad, is portrayed as one dimensional or utterly good or evil, and character development is generally well done for most of the recurring characters.
Overall: It starts off rough, but it gradually gets better and more developed as time goes on, and by game end, I can't say I regretted the experience at all, and if you can stomach the hentai scenes (or look past the ones you may not like), you'll find a very well developed story that is worth the time spent to beat it.