Summary spoilered just because this is actually a sequel book that rides very much on the events that happened in the last book! I'm planning on finishing this series because it actually fits into the few romance books I picked up off my own back and enjoyed.
That being said; this book does fall under a similar issue that most romance books seem to have with their sequels - everything is a bit more wacky, a bit more removed from reality and a bit more flandarized. I had this issue with Bridget Jones and it seems that I'm having the same problem with Don Tillman.
I think the issue is that there's no...actual problems in this book even as outlandish and insane some of them are because either Don manages to figure it out seamlessly or the author writes a solution moments after it's presented. Simsion contrives numerous 'obstacles' for Don to overcome that essentially end with 'and the person realised it was a stupid novelistic contrivance designed to eat up pages before waving Don on'.
The last book also had a ton of tropes but a ton of heart to it - I really cared about the characters and the relationship between Don and titular Rosie. I was still happy to see all the characters again - the newer characters are much more lacklustre and I'm wondering if the author received complaints about a certain character in the last book because they have been completely rewritten and their questionable personality traits have been redacted completely.
Oh and there's a 'character has to pretend to be another character' plotline. And a 'character runs to the airport' bit. Generally it's just a lot more of a generic compared to the first book. I'm still hopeful for the next book.