Byousoku 5 Centimeter, Otona Joshi no Anime Time Recommendations
Must watch for fans one way or the other.
There are just so many similarities.
Both series contains realistic depiction of problems that people might face in their lives and great illustration of their mental state and changes while confronting the problems. In addition, the music and art style are excellent and very suited for these slice of life stories.
Otona Joshi is more oriented to mature audience, while 5 cm/s is perhaps more suited to younger and older alike.