I came to read this after the anime movie, left me with mixed feelings, the setting was very different and interesting for your usual romantic story, but the pacing of the movie didnt let the story get the needed development for it to become something more.

Enters the manga, 2 years after the movie was released.
The plotline didnt change much from the movie, but was extend enough, there is alot more development for the beggining, before Mikako goes into space, there are some new faces and situations, but all in all it follows the anime story, uses its potential to the fullest and manages to give an ending, that was way more meaningfull for the romance. It expands from where the original ended, going further, to give a much better sense of conclusion than the original ever managed to.
If you are new to the story, with the manga, I believe it wont be as meaningfull, as if you had seen the movie, but it will definitly be very much worthy if those hours you put on reading it.

Also I enjoyed the cast way more with the manga, they felt more developed and well based, as humans, they were more believeable, so you kinda connect to their personal stories and the romance, much better. Thus there were some really emotional scenes, to which the art of the manga really helps to delvier
The art was also a good improvement!! The designs look way better.
It is simple, yet powerfully conveys the message the story pretend to transmit.

So I came to read it biased from what I thought of the movie, and I did enjoyed it greatly. (I still think you will enjoy the manga, you dont need to see the movie first for that)

It is kinda rare to find an adaptation that surpasses the original material, but here, it happened, and I am really glad for that! The mangaka picked the series and gave it its final touch, soo much needed to fulfill the potential the anime had left to be explored. Truly a good example of how great, adaptations can be.
An unpolished gem, that now shines much brighter!