There is a certain point in bk 3 where it just takes off. You will know it when you get there.
4 is all fun and the series remains so throughout up to Peace Talks for me. Battle Ground has been fun I just don’t like that it was split between the two books. Happy to give Butcher more $ don’t get me wrong but this really could have been 1 book even if a little larger then the typical Dresden book.