It's obvious the script is made of various books, and not always very well tied together, but overall it's a superbly made period drama with a great perf from Mortensen. In terms of structure, it almost reminded me of "Barry Lyndon": it doesn't try to be an action movie, rather span the military years of Capitan Alatriste.
This is not a movie. There is no plot, they simply took some disjointed episodes out of various novels to fill the (too long) running time, this is a shame because the source material is good, Mortensen is great and the single episodes are well done. At least you can see this as a sort of demo for Perez-Revert's novels.