The actual naval battles of the Persian invasion did involve the Greeks using maneuverable boats and guerrilla tactics. Persians were the zerg rushers of their day, as this had pretty much worked everywhere else for them. The little known or celebrated fact is that the series of naval engagements that went on during the Battle of Thermopile were way more devastating to the Persian invasion than just about anything else they experienced in that war. This movie just hollywooded it up.
I enjoyed the movie for what it was, but it lacked the newness and impact of the original movie, which hurt it a lot. I am not sure if there will be a third, but if there is one and it covers the larger land engagements, I am in for that one. Its not a great movie, but it was worth the money for a night out with the wife, which puts it above Pacific Rim Job for us.