It's about a girl who can see ghosts. I like it and it has some good emotional material, but it's basically a lightweight adaptation of a four-panel gag manga.
The main character is Amami Hibiki, an almost painfully kind-hearted schoolgirl who can see the dead. She's so saintly that she'll make herself ill doing things for her friends. (She doesn't distinguish between living and dead ones.) They'll sometimes beg her to think more selfishly. Anyway, you can think of Amami as a supernatural Geiger counter. If there's anything spectral in the vicinity, she'll have a gentle conversation with it... and you'd never believe how thick the air generally is with invisible people. Amami can take half an hour to walk down a fairly short corridor.
I'm fond of Amami. She's terribly nice. It's her schoolfriends (i.e. the living ones) I'm less enthusiastic about, although they're nice too. Unfortunately their characterisation is shallow, showing up the series's four-panel roots. Most of the time they're just punchline generators. They follow Amami around, showing no motivation or dramatic drive. They say their lines. There are occasional exceptions to this rule, but even so I basically think this show needed fewer friends and/or more character development for them. In order of dramatic significance:
1. Narumi Inoue, tsundere and lesbian love interest. This isn't portrayed clearly at all, usually being just very mild ambiguity that you'd have to be generous to call subtext, but there are a couple of scenes that play it more definitely. The clearest sign is that the other characters comment on it. Despite what I just said, Inoue actually is a character. You wouldn't call her deep, but she's scared of ghosts (which gets old, to be honest) and she's dramatically significant in ep.3 and ep.12. Unfortunately in early episodes her fear manifests as denial and stupidity, as she insists that the supernatural isn't real even when poltergeist activity is partying the night away on all sides.
2. Kana Uehara, who likes taking ghost photos on her phone. (A phone camera is as effective as Amami at revealing the dead, according to this series, but I'm sure that wouldn't work without Amami nearby.) I hesitate to rank Uehara second because she's normally just a Generic Blonde Snarky Schoolgirl, but she gets meaningful character development in ep.6.
3. Kyoko Esumi, an ex-hooligan. Her only story function is to be comedically irritable and hit Yamada, but at least you can recognise her. She and Uehara also have silly-looking transparent gel-like hair over their left and right eyes respectively.
4. Kenta Yamada, idiot and token male.
5. Makoto Ogawa, who collects zombie dolls and has a particularly high-pitched voice. That's the sum of her personality.
Visually, the show's... okay. The characters can look a little potato-faced and the show uses lots of hybrid CGI backgrounds.
That said, though, the dead are more fun. There's more variation among them, for a start. There's a samurai, a trashy 1980s "gal", a disembodied murder victim and a filthy-minded cat. (The latter might just be an ordinary cat, since Amami claims to be able to talk to animals, but it's so single-minded in its perversion that I think it must be a dirty old man who got reincarnated.)
Then there's Amami's family. Her father is just as scared of ghosts as Inoue, except that from him it's funny. Maybe it's simply because he comes across as a more rounded, human character? The story of him and his late wife is both funny and touching. "The first words she spoke to me were in pigeon." That made me laugh, but on the other hand she's psychic and so we also get a scene of her apologising for her future death.
Another thing I really like, though, is that a significant of them are from horror stories. They never do anything, unless you count occasionally dragging Amami into a graveyard by her feet. However I still like the punch that comes from this genre mash-up, doing theoretically scary ghosts in what's otherwise a completely harmless series. Ep.1 and ep.13 have cameos for Toshio from Ju-on, which would have normally meant a horrifying death for all the cast. In ep.2, Amami befriends a faceless Umbrella Girl who kills people and steals their faces. (They walk home together.) In ep.4, groping, disembodied hands repeatedly drown Perverted Cat. (This supports my theory that he's already dead in some sense, although admittedly it's just as likely that I'm taking some silly comedy scenes too seriously.)
It's a schizophrenic show. Half the time it's throwaway semi-jokes about ghosts, filtered through a likeable lead character and her underwritten friends. However it's also capable of telling emotional stories about dead people who can't pass on, or their surviving relatives who can't cope with their loss. All of these I liked a lot.
Sometimes they're understated bits like Umbrella Girl in ep.2, in which we're being invited to empathise with a monster and watch someone showing it consideration for the first time in its unlife. "She comes out on rainy days because she likes the rain."
Sometimes they're about simple, everyday kinds of grief, e.g. Inoue's little brother for their grandmother in ep.3.
Sometimes, though, they're about dead children (eps.1,8) or daughters (eps.6,11). These can be particularly strong. They could have been annihilating if the show had had a more consistent tone and a better-written regular supporting cast. Even Amami herself doesn't have the emotional punch that I think she should have had, since the tone's too light for her problems to have much weight and her saintliness has no dramatic cost, so it doesn't really feel earned.
I'm in two minds about this show. It's not very good, but I really like what it's saying when it takes its themes seriously and starts telling stories about them. Be nice to ghosts. Scary strange spooky things are people too. Should I be suggesting that you just cherry-pick the best episodes? I wouldn't call the show marathonable, which suggests that it's more throwaway or disposable than it might have been. I do like it, though. I prefer the version of it in my head to the the reality, but I'm modestly fond of the latter too.
I've noticed a few 2015 anime about coming to terms with death. Death Parade and Plastic Memories are two that spring to mind. Re-Kan! is more lightweight than either of those, but it's covering similar themes in its own way. You'd expect a stronger anime to have come out of these ideas, but even so the show has deceptive strengths and a certain amount of charm.