I really liked this book (so much so that I picked up the second book the day after I finished the first one).
As with any book that has constantly alternating points of view, I found it distracting at first but eventually I was able to settle into it. (It's a personal preference. It works for some people and not for others). The world is an interesting place, though I think the nonstandard measurement of time is unnecessary and irritating.
I did not guess the connection between Mildmay and Felix, though there were enough clues that it doesn't feel like it's out of left field.
In the beginning I was more interested in reading things from Felix's point of view. He was educated, snarky, and spoke proper English. After he became mad it was more interesting to read things from a madman's point of view. Unfortunately, Felix's madness limited his autonomy so after a while my alliegence shifted and I preferred reading Mildmay's point of view because Felix's felt reptitive. (He's afraid of monsters, he cries).
It took a little while to get over Mildmay's grammar (or lack thereof). I think it fit the character, it's just another of those things that can drive me crazy. By the end of the book I liked Mildmay at least as much as Felix, if not more.
The journey east was interesting. I liked the secondary characters, especially Giddeon. The magic system is interesting and the world is rich and complex.