A very nice ending indeed, got quite teary-eyed.
Very good anime overall x)
EDIT : I was really surprised by Kaori's letter though, I know she had some feelings for Arima, but did not think she had had them from the beginning.. And I feel kinda bad for Watari, because he had clearly fell in love with her (in my opinion anyway, we see him keeping a picture of both of them as a background in his phone..).