I didn't detect any overt message in it. I think the mark of a good story is that all dimensions are shown, and the individual reader can read into it what they want.
As for me, my favorite quote is from Titus Pullo. After Vorennus's scouting party crosses the Rubicon, and Vorennus complains the Republic is under attack and he is traitor, Pullo responds that the sky still stands and the earth remains. Yes. Life goes on - it may be a different dance but you still have to dance.
For me the politics was a backdrop that effected the characters' personal lives and their relations with each other. The center of the show was not in fact the historical figures, but the two Roman everymen - LV and TP. At the end of Season 1, LV's involvement in politics and wars deprives him of everything he holds dear - his family and his dignity. At the end of Season 1, TP finds he is to give up his wild ways and find meaning by settling down with his lovely slave girl.
I must say that the series- of which I have seen just seen season 1,ending with the assasination of Caesar, is admirable. Being a commercial series it submits to some cliches about Rome as opposed to the more academically oriented BBC's Roman Empire 6 episodes ,each devoted to certain top historical personalities. Instead Rome focuses except the machinations of the rich eg Caesar and his circle, to the lives of two average Romans, Vorenus and Pullo.But replying to the first message about the politics one must not overstimate the Republic which according to sources was never much of a Republic, dominated by a Senate, a very aristocratic body and essentially a self-perpetuating oligarchy. Note in the last episode of the first season the dismay of Brutus and his circle at the introduction of Gauls in the Senate as well as the elevation of a plebs Vorenus to the rank of a Senator. All this democratization of the Senate was the work of an autocrat, Caesar. One should idealize the Republican period as a democratic one since a very distinct oligarchy lurked behind the facade. One must not blame Augustus and his Principate. I do not think that he made the world a worse place for the average inhabitant of the Empire by turning the Republic to a Principate. The Republic was wildly clientelistic and you can see this process when Vorenus receives his clients-a micro-scale since Vorenus is just a minor magistrate then. Also do not forget that the whole reputed system of Roman law operated in the case you were a Roman citizen rich or poor-remember the spokesman's proclamation: true roman bread for true Romans.So the Republic was good if you were a Roman. How many of the Inhabitants of the Roman controlled Oecumene were citizens during the Republic? Can A statistician enlight us? I think a book by Garnsey about the Roman Empire has an answer, But I must say that I by heart rember a certain sentence that about the time of Augustus the fully-fledged beneficaries of the Roman legal system -that is those that could fully exercise the rights presrcibed by it were a shocking 1% of ther population! And do not forget that already by the time of the constitution ascribed to Servius the system of vote in the comitia centuriata-the assembly of the people gave the majority to the curiae of the first class with those of the knights at the expense of the rest four classes plus the class of the ploletarians. So another reason not to idealize the Republic.I think the series is accurate, for most of the people darkness was followed by darkness.