It's lovely. One of the best live-action films based on a manga/anime I can remember seeing.
The anime's probably still better, mind you. It's more in-depth, with more story. This lets it explores its ideas in more detail, e.g. the fact that Kaori's weekly memory-reset only deletes any memory of friends. If you're family, a teacher, a disinterested stranger, etc. then she'll remember you. This makes sense of something that's puzzling in this film, viz. everyone's determination that Kaori shouldn't make friends. The doctors had said it was best for her, yes, but even so I had trouble accepting on this unimpressive level of explanation that Kaori's loved ones could have so easily accepted that it was right to reject friendship. That's just unhealthy. Had that been me, I'd have announced it to everyone on transferring into school, thus preventing difficulties later. "My name's Kaori Fujimiya and my memory resets every weekend." Okay, yeah, she'd had unpleasantness at her last school... but even so.
That said, though, this film has lots of great things. These include:
1. Kento Yamazaki as Yuki Hase, the boy who's determined to be Kaori's friend. What's more, he means it. He's not trying to get into her knickers. He really does just want to be friends, although of course his feelings will deepen eventually. Yamazaki is this film's secret weapon. He's so happy and upbeat all the time. Admittedly that's the role as written, but he makes it work. He can even play crushing disappointment while being charming and upbeat. I'm pretty sure the actor's mostly just playing himself and this isn't an acting masterpiece in that sense, but even so I shouldn't think it's possible not to fall in love with Yamazaki's performance here.
2. Haruna Kawaguchi is pretty good as Kaori Fujimiya. (She's also beautiful when she smiles.) Admittedly she's not as great as Yamazaki, not being able to bring enough power for her two heavyweight moments. However she's solid and very likeable 99% of the time, making for a central duo that I could have watched all day.
3. A premise that's perfect for live-action. I'd been champing at the bit to see this film for ages. Some manga are better-suited than others to becoming a film. You'd need optimism to have high hopes for, say, a live-action film of Tenchi Muyo or Fist of the North Star. This, though, you'd have to be some kind of genius to mess up. It's so simple and distinctive (although admittedly not without precedent elsewhere).
The first half is the more distinctive. Yamazaki's persistence in the face of repeated rejection is fun, charming and unique. The second half is more conventional teenage relationship stuff. It's still excellently done, mind you, but it's more reminiscent of lots of other films and you'll have a better idea of where you expect the plot to be going. (Kujou also seems like an idiot. Seeing Kaori get hospitalised should have rung some kind of alarm bell, surely, even if you wouldn't expect him to guess the exact situation.) That said, mind you, I like the way that the film takes its time and plays each story beat more fully and sincerely than I'd been expecting. Instead of trying to cram in lots and lots of the original manga, they've been selective.
The notebook kept making me nervous, incidentally. I wanted them to make electronic back-ups, but of course it's a handwritten notebook. What about photocopies, then?
It's a charming film, but not a saccharine one. People can be nasty, even if they don't mean it, and Kaori's pretty fragile. Her condition is clearly rooted in some kind of trauma and she's capable of getting head pain or collapsing if you say the wrong thing to her. However I loved both her and Yamazaki. The ending hit the mark for me. This film's good enough to make you wish there was an English-language DVD, because you'll know someone who'd have loved this as a Christmas present.