5 Centimeters, I would definitely recommend. I can't help but repeat what everyone else has said about the sadness factor. This movie's a pet favourite of mine. I've gone so far as to limit myself to watching it too many times this year to avoid getting bored of it.
Anyway, like others before me have said, this movie packs an extremely strong emotional punch wrapped around excellent, almost photorealistic, scenery, an amazing soundtrack which accentuates the moments of emotion which we see so much during the entire movie, and an amazingly realistic plot line.
It is incredibly sad, but I will still recommend this movie to you despite warnings of not for the faint-hearted because this isn't meaningless weeping. It's real life. This movie emulates real life so well that I almost died during the movie. I literally (Yes literally, and not figuratively) felt my heart wrench during one part. And that wasn't even at the climax. It was just the first episode. You can really sympathize with the characters despite only having been introduced to them for five minutes or so.
This movie is the culmination of the beauty and tragedy of existence that I would really, really, recommend you to watch it. It makes you think. And, if you've been through what the protagonists have been through before, it'll make you reflect on those moments which you might have done better. Choices you could have made.
I guess, the only con with this movie is that it's a bit too slow for some people. Some people. If you're used to action sequences, don't hope for any of that in 5 Cm. I mean, the movie doesn't even try to exxagerate the plot for greater effect. Sure there's some pretty awesome camera work, but that's as far as they go in making it seem larger than life. The plot seems like something that happens everyday and yet we just don't see it because it doesn't always happen to us.
/End Sappy Review.
I'm sad now. I watched this movie a few months ago and it still brings tears to my eyes.