This  story was sweet, but if you've read John Green's "A Fault In Our Stars" then you will find it very familiar. 

Despite the 16+ age of the characters and themes of terminal illness and grief the story covered, I found it overall quite childish. I think for the target audience it probably isn't so much of an issue, but the good girl/bad boy romance dynamic was so clichéd and I found the 'whirlwind' love cringy. 
Despite this, the characters were mostly likeable and the tight-knit, family nature of the hospital setting brought enough  dimension to Stella's that she felt believable - helped by the fact that she was interesting outside of her relationship to Will, we got a sense of her whole life, rather than only engaging with her as her illness.

This is a done before, but likeable non-the-less quick read.