At lot of people seem to see this as complete representation of the mange or even the story of Nana and Kaoru. And although this might have been the starting point it is not the end result. What we have here are 2.5 moments out of the mange as anime instead of an adaptation. If you - have not read - the mange this will make no sense as, like other people pointed out, there is no story and you don't see their relationship develop. If you - have read - than this will be a nicely done representation of 2.5 moments out of the first part of themanga.

And if you see it as that it really shines.
(If you, you will not enjoy this)