Almost indistinguishable from the manga. It's a faithful adaptation, with the only noticeable differences being fewer nipples in the broadcast TV version (to be fixed in the Blu-ray release) and some shuffling of the manga chapter order.
Thus it's still fanservice harem nonsense. However I had fun with it and I hope they make a second season.
The premise, as usual, is that Kimihito is the one-man host family for a bunch of monsters. (At first there's only one, but they accumulate.) They're exchange students visiting the human world. Japan recently passed some eccentric laws to allow this, although the wrinkles in these would have needed ironing out even if their implementation weren't currently in the hands of lazy, responsibility-dodging officials.
Anyway, Kimihito's students are all female and they all fancy the arse off him, but (a) any of them could accidentally kill him at any moment, and (b) sex with an exchange student is punishable by deportation. In fairness, real-life exchange programs generally have similar policies. Kimihito's students will eventually include Miia (lamia, i.e. a snake), Papi (harpy), Centorea (centaur), Rachnera (spider), Suu (slime), Mero (mermaid) and Lala (a dullahan). Almost all of them have big boobs and a tendency to have wardrobe malfunctions. (In some cases, admittedly, this is logical.) Their monster biology has been thought through quite well, which is interesting, but at root it's still a bunch of hot girls focusing single-mindedly on one bloke.
In other words, unhealthy wank fantasy for relationship-challenged otaku.
That's ignoring the show's other monsters, by the way. One thing I hadn't noticed and can only be seen from her profile page is that Doppel isn't the doppelganger she claims to be, but an eldritch abomination whose true appearance, name and even language are beyond human comprehension. I think it's implied that she's Nyarlathotep, the Crawling Chaos, albeit an even less dangerous one than Nyaru-ko from Haiyore Nyaruko-san. Note her tentacle-like hair, for instance. Not only is it prehensile and used to make her disguises, but in the end credits she uses it for locomotion.
The monster side of the show is great. It makes the show such obvious fantasy that you'd feel silly taking the harem stuff seriously, but it's also quite well developed. It's specific about its sources, for instances. Lots of the monsters are from classical mythology. Tio isn't an oni, despite appearances, but an ogre (of which oni are a sub-species, according to her profile page). Mero is a western mermaid rather than a Japanese one, which would have been a whole lot nastier. (The odd one out is Suu the Slime, which is an invention of the modern gaming industry rather than folklore.)
They're also every bit as dangerous as they'd be in real life. Kimihito's life with them is no easy ride. If Miia forgets herself, she'll crush your bones. Centorea couldn't be more high-minded, but she's still basically a horse and capable of kicking, trampling and worse. Rachnera has more control over her strength than the other girls, but she's also a sadist who'll bind you and leave you dangling from the ceiling for fun. Even the childlike Papi has claws that can crush floorboards, while the amiably semi-sentient Suu is arguably the scariest of them all, if you catch her at the wrong time. Note that technically she'll have started digesting anything she's been in contact with for too long.
The only monster-related thing I didn't like was the animation of Miia, whose movement wasn't snake-like enough for me. (She moves like an octopus tentacle.) I stopped worrying about that after a few episodes, though. Ideally I'd have also preferred Zombina's character design to be more zombie-like, but that's not the anime's fault since they're just following the manga. She doesn't look dead at all. She's more like Frankenstein's monster, with body parts falling off and having to be sewn on again.
The fanservice, on the other hand, is both over-the-top and insufficient. It's been censored from the manga, which occasionally means losing the money shot for a joke. You want to be watching the Blu-ray version, when it comes out. However it's still outrageous and shameless exploitation.
It's a lightweight show. It's fun. There are dark implications to its worldbuilding if you think about it, but in practice everything's charming and being played for laughs. I wouldn't have minded something more dramatic, to be honest. Rachnera's backstory is tragic (although some of it's in a later chapter) and the character is borderline evil, but in practice we don't care because she doesn't. She joins the harem almost immediately instead of being a temporary villain and thereafter just shrugs everything off and has a laugh tying people up for bondage comedy. Other potential antagonists (e.g. the orc terrorists, the various "D"s) and every major problem gets a simple, consequence-free resolution.
It works, though. It's not the show it could have been, but it's funny and very watchable.
The chapter reordering is intelligent, by the way. Each anime episode is adapting two manga chapters, so sometimes they'll shuffle the chapters into pairs that fit together better. One chapter (17) doesn't get adapted at all, which means we're never introduced to Polt the Kobold. Can't say I'm fussed about that. After a few episodes I started playing "guess the new chapter order" but I usually got it wrong. I think the anime's choices were better than mine.
The tiny differences are sometimes significant. Ep.2 of the anime portrays the "forget everything in three seconds" joke (which is a real Japanese phrase) better than the manga did. Papi's very funny in that episode. Eps 3 and 9 spend slightly longer on the sex gags, in the latter episode at the expense of character business that I thought was better. I'm not a fan of ep.9, to be honest.
I like this franchise. I probably shouldn't, but I do. I'm fond of it, although its fanservice can be eye-rolling or at worst slightly distasteful (e.g. shots of Papi's arse). I think Kimihito's theoretically destined for Miia, effectively getting two sex scenes with her, but it's all academic after we've hit the harem. Centorea and Rachnera are clearly the characters with the most depth. The "embrace monsters as people" is a worthwhile theme for the series, I think, and the cast are likeable. Fingers crossed for a second season!