My exact thoughts on ryeon-gil couple and definitely agree about ryungoo's closure, he had a heartful talk with his mom which was what I anticipated for the ryeon-gil couple. And, we didn't really get an insight as to why jungil chose to be a reaper and not look for his wife.
I think Jung Gil was going to look at her book, but realized he can't without authorization. Then, he decided to look at his own book, but realized that it was locked the 1st lifetime and also realized that Koo Ryeon's was locked. Both were locked to keep Jung Gil from finding out about the past. But, I still don't understand why he decided to erase his past instead of looking for Koo Ryeon when he loved her so much.
I actually like that the Nut in this version is not as arrogant as the previous versions which were reasons why I didn't really like the FL.