If you look at it in the grand scheme of things, PM was always going to be a slower story than we'd been used to with Eps 4-6 - you have to remember that it was setting up what is essentially a 13 hour story.
Once Ep III has been released, I'm in two minds about what order they should be watched - in some ways, I think it'd be good to watch them 1-2-3-4-5-6, but at the same time, seeing 1-2-3 before 4-5-6, there's a few plot twists, like "Obi-Wan never told you what happened to your father" that I think you should watch before you see where it all started.
:? Decisions, decisions.