I thought Felix and Henry were sweet together. Felix likes to help people, and when Henry turned up at the gym with his daughter in need of help, Felix made it his mission to do that. Even if Henry wasn't very receptive to it at first. But Felix worked his way in and earned Henry's trust, and the way they came together (with all the other characters we've met over the series) to help with Henry's daughter, Hazel, was very sweet. 

I didn't love how the subject of Hazel's mom was handled. A few aspects of that kind of gave me the ick. But outside of that, I think I liked this one best out of the series so far, in terms of the main characters and the single dad bit.

For the first two books, I felt like the narrators were miscast (they should have swapped), but book 3 worked for me, and I thought they gave the correct role to the correct narrator this time, too.