I liked the pairing of Amandla Stenberg and Nick Robinson. While I haven't seen much of Stenberg outside the Hunger Games, she was good in the role of Maddy. Nick Robinson was good here, although a bit two-dimensional. It took me a little time to buy the chemistry between the two, but as solo performers, they seem perfectly cast for their roles.
The story reminds me of Bubble Boy (the movie with Jake Gyllenhaal), and to an extent, it is a modern version of Bubble Boy. The romance was also quickly developed, but I liked how they had conversations in the dioramas Maddy has made. Since they don't communicate face to face, having them in that setting gives an added bonus to the movie. There isn't much character development either, but this was very much plot-based.
As far as adaptations go, this was alright. I wasn't expecting a grand scale of drama between the characters, but this wasn't a terrible one either. Some aspects, particularly Maddy's relationship with her mom, was underdeveloped. However, if you're only here for the story between the two teens, there's nothing to be disappointed about.