It's rather nice. It's a shoujo (i.e. for girls) romance that's more intelligent than it needed to be. It doesn't have a conclusive resolution, but then again the manga it's adapting was still running at the time.
Our heroine is Yoshioka Futaba. Three years ago, she was fond of a kind, gentle boy called Tanaka Kou. She was like that too. They'd have made a good couple. Ep.1 starts with them sheltering from the rain together, rendered in dream-like watercolours. They even make a promise to meet up on what's, effectively, like a date.
Now they're both in high school, but they've changed. Kou never showed up for that date. He disappeared. Now he's a blunt, apathetic loner who's going downhill academically and doesn't even use the same surname as before. He tells Futaba that he's no longer interested in her and finds her questions about his old self annoying. That said, though, Futaba has changed too. She's jettisoned her old personality and has deliberately turned herself into a slob. Being popular with the boys in her class had made her unpopular with the girls. She wanted friends, so now she eats like a pig  and hangs out with people Kou describes as "friends in name only".
 by Japanese standards
What's interesting is how much character development is packed into this show, above all for Futaba. Ep.2 has her facing up to so much about her life that it would have been a decent series finale. She reinvents herself twice. The manga author, Io Sakisaka, created the series to explore the process of growing up, i.e. teenagers making mistakes, picking themselves up afterwards and learning from them. The characters all grow up in their own ways. They create identities for themselves and don't always even like them, but can still feel trapped inside these self-inflicted shells anyway.
Futaba does this a lot, which if badly handled could have made the show hard to watch. It's not. She's always likeable. She cares a lot for her friends and it'll eat her up if she thinks she's not doing the right thing. More than once, she'll be completely honest with her friends and makes herself say things that you'd half-expect her to keep a guilty secret. I respected her for that. Her relationship with Yuuri is a particularly strong element of the show, especially given the ways in which she mirrors Futaba.
Kou is harder to embrace, partly because we're seeing the world through Futaba's eyes and she doesn't understand him either. Sometimes he'll be helpful and supportive. Sometimes he's cold and deliberately pushing everyone away. He's doing himself no good. He's sending mixed signals, to put it mildly, but it's pretty clear that he's damaged and at some point we're going to learn what happened.
I mentioned the intelligence. The characters' thought processes and motivations are quite subtle. You could tell a perfectly good version of this story with exactly the same plot, but fewer layers in the underlying emotions. I'd watch that show. I'd enjoy it. However this one is better and steers further away from cliches.
There are interesting themes here. There's the one about wanting to fit in with the crowd and put on the right face, which very much describes Futaba at the beginning. There's friendship (true, false and other flavours). There's having the strength to change yourself, even if you don't like the way you are and actually want to change.
The art is... occasionally not very good. It has little moments that make me think the original manga can't have been particularly well drawn. However I was wrong. In fact the manga looks pretty good and the anime is being very faithful to it, to the extent of keeping one or two images that look a little flat. I respect fidelity. Sakisaka's character designs in particular are pretty much unchanged, being more realistic than in a lot of shoujo.
Even the two OVAs are very good, which is unusual for OVAs. They're not wheel-spinning filler, but instead are adapting more of Sakisaka's original manga.
Ep.0 is putting together the complete story of Futaba and Kou in junior high school, three years ago. Thus we've seen chunks of it before, in the main series flashbacks, although this time without the psychedelic watercolour backgrounds. However it stops being a recap and acquires a reason to exist when we hit the 7pm assignment in the park and Futaba's emotions afterwards. This would be a sad episode if we didn't know the rest of the series was coming next.
Ep.13 is arguably a better finale than the TV series finale, ep.12, although you can also see it setting up future storylines if you know what's coming after this in the manga. It's very good. Futaba and Touma made me laugh, but among other things it's also a huge Yuuri episode. If you've just watched the TV episodes, definitely try to see this too.
It's a strong series, I think. It doesn't significantly diverge from the expected patterns of shoujo romance, but I think it's more intelligent and has more character development than it could have had. As an anime it's incomplete and I'd have enjoyed it more with a clearer resolution, but it still reaches a nice place to end. Besides, I shouldn't judge without watching the OVAs. I watched this partly because I knew it had also been adapted into a live-action movie, but in fact shoujo manga are comparatively unlikely to get an anime adaptation these days and it had recently been more common for them to get turned into live-action instead. This show broke through that barrier and achieved both. I liked it a lot. Maybe I should read the manga too?