An interesting book. I like the way that (some aspects of) the Spartan culture was presented - the "outsider who grew up in the system" mechanism worked well, as did the choice to have the narrator retell the story to his captors. The arrangement let the narrator skip around in time a little, presenting vignettes to illustrate a particular point in order of interest, rather than chronology.
I found the book started a little slow, but I was completely engrossed by the description of the first clash between the Greeks and Persians - unwilling to put the book down until it was done, even though it was time to go to work. Thereafter, my interest remained high, although it never quite reached that peak again.
Pressfield knows his way around the English language - the sentences were well crafted, and a joy to read. The only exception to this is his choice to repurpose a popular English vulgarity to mean something else (and I'd argue not particularly related), explain that a few pages later, and then shortly thereafter use the word for its traditional meaning. I didn't really see the point of that, and it was a little jarring. Still, that's a fairly minor quibble, and I'd strongly recommend the book to anyone interested in historical fiction, especially historical war-ish fiction.