It's a laugh. I enjoyed it.
Umaru has two personas and three identities. We all do this, but Umaru's version of this is more extreme than most people's. "Outdoor Umaru" is beautiful, clever, modest and perfect in every way. She's top in every subject at school. "Indoor Umaru", on the other hand, is a lazy game-obsessed slob who lives on junk food and mooches off her brother like a parasite.
People who know about "Indoor Umaru" = her brother.
People who only know "Outdoor Umaru" = everyone else.
Oh, and there's also a third Umaru called "UMR", who goes out in public in disguise to play arcade games and doesn't even answer to her real name. She's "UMR". That's the alias she uses when entering her fearsome top scores.
Umaru is a terrible person. This goes without saying. However she's also funny and sufficiently likeable in her shameless bad behaviour to carry the show. She's a manipulative brat who lives to badger her brother Taihei, but it's also clear that both of them would be deeply unhappy if the other stopped being there. Umaru pestering Taihei is what keeps them both going. They're very fond of each other. It's just that Umaru's motivations are, in order:
(a) behave badly
(b) maintain the facade of "Outside Umaru"
Umaru's personalities are also indicated by an art shift. "Outdoor Umaru" is drawn like a standard realistic anime girl, while "Indoor Umaru" is drawn cartoonishly. She's a tiny grinning lump in a hamster hoodie, only about knee-high to her normal self. At times it even seems possible that the show is regarding this as a physical metamorphosis, but personally I ignore that possibility because I think it's funnier if Umaru really is the same Umaru throughout and it's just her Jekyll-and-Hyde personalities that stop people from recognising her.
On its own, all this is fun. It made me laugh. However it becomes livelier still when it develops into a four-girl show, with Umaru acquiring friends who reflect her situation in their own ways. Each girl has different public and private personas and is prone to being misunderstood. Each girl also has a big brother, although Ebina's is only in the original manga and here there's only the subtlest of hints at his existence. (Maybe we'll meet him if the anime gets a second season?) As for the other big brothers, they're colleagues and sit next to each other at work.
EBINA - a girl with no self-confidence and a strong Akita accent that she tries to hide. Has a crush on Taihei because he's nice and doesn't stare at her boobs, but it'll take a miracle to get her to do anything about it. Her default mode is "flustered and nervous", so the way of telling that she's even more stressed than usual is to look for steam coming from her head. (Also, Taihei appears to be asexual. His boss at work has been pursuing him very obviously for ten years and Taihei still hasn't noticed.)
Ebina is friends with "Outdoor Umaru" and has no idea that any other version exists. She's also the only cast member who's not an ace at school (which is another hit to her confidence), although the thick-as-a-brick Bomber would presumably come below her if he weren't now in the world of work.
SYLPHYNFORD TACHIBANA - wildly competitive self-appointed rival who wants to beat "Outdoor Umaru" at everything, but becomes friends with "UMR". Sylphynford's the exact opposite of Umaru when it comes to her fake personality, acting like a total loon in front of everyone but her big brother Alex. If she ever becomes aware of his presence, she'll become a hero-worshipping shrinking violet who'd sooner die than seem not to be perfect.
KIRIE - the biggest weirdo in the cast. Everyone's terrified of her. She snarls and glares at the world and has the air of being about to beat you up. In fact, though, she's just shy and can only relax when talking to children. Fortunately "Indoor Umaru" is as childish as the sun is hot and about the size of a four-year-old, so Kirie calls her "master". Kirie also hasn't realised that this is the same person as "Outdoor Umaru", on whom Kirie has a massive lesbian crush (while being incapable of speaking to her).
Kirie's big brother is a dim, good-natured doofus called Bomber who loves his 1970s hairdo. He gets on fantastically with "Indoor Umaru", but it would be a catastrophe if they ever started a relationship. They'd be a radioactive black hole of happy-go-lucky. They'd starve to death when the fridge ran dry of junk food and cola. Kirie isn't shy with Bomber, but she makes up for this by being aggressive, hostile and violent.
This isn't a serious show. It's just fun. The romantic stuff isn't going anywhere, but you don't expect it to. It would be nice if Taihei woke up to Ebina one day, but then again if he did, you'd feel bad for his boss Kanau. My favourite character here is Kirie. The show made me laugh almost immediately with Umaru's transformation at the start of the first episode, but like Monthly Girls' Nozaki-kun (its Doga Kobo stablemate), that first episode isn't the funniest because the supporting cast haven't shown up yet. I don't think it's as good as Monthly Girls' Nozaki-kun, by the way, but they're both slice-of-life anime comedies with a school setting, a central pair of eccentrics and their yet more dysfunctional friends. They're also both very entertaining.
It would have been possible to give this material more depth, given how weird and messed-up much of the cast are. That said, though, any show built around Umaru and Taihei was almost guaranteed to be goofball comedy. It's light-hearted fun. I think it makes its gleefully appalling main character both attention-grabbing and likeable, although I bet there will be people who disagree. I'd say it's well worth a look, at least.