This is the second Taylor Jenkins Reid book I have read and I have fairly similar thoughts this time around. I still enjoy TJRs writing style, but find her books tricky to navigate without chapter titles or numbers - but that's more me being frustrated while trying to buddy read without spoiling anything. 
I thought the Sliding Doors-esque storyline was a really entertaining reading experience, and I truly loved the first half of the book...
<Spoiler> ...but when that pregnancy trope showed up, it honestly hurt my brain. It was fine in the end, but it wasn't something I was prepared for or really looking for.
Hannah's story/stories(?) resonated with me, so I was attached to her as a character and her experiences, which meant her inner monologue was so relatable to me. I don't think there was a character I didn't like barring Mark of course, since that was by design, but even he wasn't "hate-able". 
Overall I thought it was good! I probably won't read it again, and I think I may be done with TJR for now, but might pick up something else of hers in the future. 

Some trigger warnings for this story that you should look into if you struggle with reading about:
Car accidents 
Injury trauma and brief injury descriptions
Hospital environments
Pregnancy and pregnancy loss
Divorce