So far, so good. The series is supposed to pick up pace after the first couple of episodes when characters and plot complications are well-established in the viewers' minds.
What HBO shows do that is unusual is they develop the secondary characters in a series a lot more deeply and richly: even the bit players make you stop and think about them for a while. You definitely see that in shows like The Sopranos and Deadwood, and I think you'll see that happen in Rome, as well.
I guess the only downside is if you're remotely familiar with Roman history, some of the suspense will be kind of taken away: Pompey is going down, Brutus betrays Caesar, &c. &c.
If they do film a second season to take place some time later, I guess they would have to pull a Star Wars and re-cast Octavian as someone a bit older as he goes up against Marc Antony for all the marbles...