"I was left wondering what the book was about, frankly"

Precisely: there didn't seem much point to it, and the story wasn't a fully formed story.

"I liked Club Dumas well enough but preferred the movie they made from it (The 9th Gate)."

I swing backward and forward as to which of the two I prefer. I thought it was a pity the movie omitted the entire Dumas part of the plot.

"No more Perez-Reverte for me, probably."

I might well try another of his mystery-type books, but once was enough for Alatriste.