This is a fun lighthearted movie that reminds me of Being Erica or TNG episode called Tapestry - where you can go back in time and change past mistakes to produce an ideal outcome. As you can guess, the lesson learned is that manipulating the past does not lead to the perfect outcome. Good idea although nothing new.
What I like about the movie? Skyler Gisondo as the friend Evan IS the heart and humor of the movie. I would watch it again just for his comedic performance that kept me in stitches. I looked forward to each and every scene he was in and he did not disappoint.
What could have been better? I didn't feel the chemistry between the two main leads. I believe that part of the problem lies with how Stillman was written and partially the casting choice.
While Sophie Turner was okay as Debbie, I feel that Zooey Deschanel would have been a better choice. If I closed my eyes and just listened to the voices, it almost sounded like that's what Sophie was going for.
Asa Butterfield as Stillman came off as a bit conceited and whiny. It was hard to feel sympathy for him at any point. The scriptwriter could've made him more likeable and a different casting choice would've helped also. Maybe someone like Adrian Grenier in She Drives Me Crazy (1999)? Someone that you feel sorry for would've helped.
If the script was tweaked a little and different people cast in the leading roles, this would've easily been an 8. They didn't do anything wrong and there were genuinely funny moments, but it lacked that certain spark that could've really made it great.