It's a good movie, although it lacks of a proper conclusion and intentionally blurred the lines of its own ending.
1-star reviews are ridiculous. Both actors were adults and there is no sex-splicit scenes, no nudity. The movie plays with the imagination of the spectators the same way Cairo does when writing about her relationship with Mr. Miller.
Controversy of the age gap? Where is that controversy when we witness a bed scene between Nicole Kidman and Zach Efron? Or Cher and Maddona with her young partners? The movie is controversial for showing a relationship between a teacher and a student, like many others; but not because Jenna Ortega is younger than Martin Freeman.