I have noticed a difference in books written by journalists, compared to those written by historians. Journalists tend to focus on specific events and people, whereas historians focus on wider trends in society. This is true of this book, which focuses almost exclusively on the leaders and front bench of Fine Gael rather the the party more broadly. Some events are covered in great detail while others are skipped over completely.
The biggest weakness is the lack of analysis, the authors report what Fine Gael did and how politicians viewed the party but don't ask deeper questions on its impact on society. Perhaps the authors wanted to remain neutral by avoiding questions of success and failure, but this denies much insight to the readers.