I finished Book I today. Thucydides is more focused overall than Herodotus. Herodotus loves a good story, and will interrupt the action to provide background on some incident that may have a more or less tenuous connection to the main story. It might be argued that the delay serves, as it does in Homer, to heighten suspense. It is arguable whether or not suspense in the writing is a proper goal for an historian. While there are digressions in Thucydides, it’s arguable that they are more relevant than the digressions in Herodotus. The long stretch from 1:89 to 1:117 fills us in with the background to the period, and gives some sense of what happened between Plataea and the commencement of hostilities.
I would have to break out my old textbooks on rhetoric to provide a detailed analysis, but one noticeable feature of the speeches is that there is within each speech a reliance on thesis/antithesis. The speaker will present a hypothetical, sometimes within the format of a question, and present an immediate contradiction to that thesis.
One of the speeches, I think by the Corinthians, contrasts Athens and Sparta. Athens is said to be innovative, but it’s not clear from the context whether he means innovative in politics, or innovative in techne, mechanical skill. It seems to lead more to the former, though I think a modern reader would at first think of technical innovation.