I was excited about this one. I'm a fan of Ito Junji's horror. This anthology anime, though... well, it's interesting, but it took me about two months to reach the end.
At first, I thought Junji Ito must have a problem with endings. Reading up about him, though, I think that's an illusion created by this anime adaptation. It's fine for manga or comics to end on a shocking image. That's a Junji Ito trademark. He's built a highly acclaimed career on it. This anime, though, struggles with it. Seeing a big gross surreal thing here just makes you go "yes, and?" That's twice as true when it's the story's punchline. Ep.3a ("Boy at the Crossroads") has a non-ending, for instance. I'm sure Ito's original works better, but it sort of flops here. Ditto for ep.6a ("Window Next Door"), even though that story as a whole is so unsettling that I can easily imagine its ending freaking me out in manga.
(There are some good endings, though, e.g. ep.5a: "The Ongoing Tale of Oshikiri Collection". I wanted to see that continuing. I'd also cite ep.6b: "Gentle Goodbye".)
Another thing I didn't like was Souichi Tsuji. He's one of Ito's very few ongoing characters and he's a smug, hateful toad. Admittedly his attempted villainy always backfires and fate has it in for him in a big way, but I think I reacted to him more negatively than most. I think his misadventures are meant to be at least semi-comedic. Personally, though, I just flat-out hated him and I wanted him to die and get off my screen. (Souichi isn't the only protagonist I hated, incidentally, c.f. also the rude, unprofessional filmmakers in 2a: "Fashion Model".)
This isn't a flawless series. Its episode quality is highly variable, especially since I didn't always find it emotionally engaging. I like horror, but this is an unusual variety. It's liable to be anti-empathy, instead being more about surreal, unpleasant trips into What The Hell Land. The strongest episodes are indeed strong, but in a way that makes you want never to watch them again.
I can't deny that that's effective horror, though.
It's also worth noting that as an anthology series, you can dip in and out. There's no need to watch any given episode. Ones I'd recommend include:
Ep.3b ("Slug Girl") - it's probably too goofy to be scary, but that's why I love it. Besides, if those events actually happened, you'd be clawing at the walls of your asylum.
Ep.4a-b ("Shiver" and "Marionette Mansion") - are both good. Ep.4a has a sick girl who never leaves the house and hates bugs, then gets holes opening up all over her body. Bugs, ewwww. (And I like bugs!) There's also a creepy doctor. After that, ep.4b does unusual things with the horror cliche of puppets.
Ep.8b ("The Circus Comes to Town") is the most evil horror circus ever.
Ep.9a-b ("Painter" and "Blood-bubble Bushes"). Ep.9a got me absolutely hating that bad-mouthing artist's model... and then I realised that she's Tomie, after which I was glued to the screen. There are eight Tomie live-action films and I've seen them all. Holy shit. Here she's such a bitch that at one point this is funny. Her undead murder respawning immortality powers are probably less skin-crawling than her personality. See also the two Tomie OVAs, which are deeply nasty and unpleasant. After that, ep.9b is a sort of reinvented vampire story and really, really gross.
Ep.10a ("Greased") - made me feel slightly ill. The oil. Ugggh, the oil.
Is this a good series? In a lopsided way, yes, but it took me ages to get through it. It was never my first-choice anime and I think I'd have broken if I tried to marathon it. I'm pretty sure it's not as good as the manga. The art's good, for instance, but the animation can be ugly. The horror storytelling just doesn't resemble ordinary film or TV and so the endings only seem to work half the time. (Sometimes you can impose themes and readings, e.g. a possible drugs subtext in e.12a "Smashed", but that's likely just to be a futile attempt to retrofit reality on to something entirely unrelated. "Smashed" in particular is so wacky that I'm sure my suggested subtext was unintentional, if only since any attempt to draw a message from it would be hilarious.)
Sometimes it's super-creepy. Sometimes it's more like a trip into the Twilight Zone. Sometimes it feels as if Junji Ito is putting his bad dreams down on paper. (Bad, strange dreams.) Oh, and there's an awesome theme song.