I played as the Romans, Macedonians, and as one of the Greek states (I think the Achaean League). The game had a serious ping-pong problem where defeated troops would have to be defeated several times, bouncing between provinces, before the stack was finally eliminated. The expansion vastly improved the politics and internal management over vanilla to the point where it was actually playable. I didn't really care for the omen mechanics, and even the expanded political system caused some frustration.
As far as military recommendations, amass heavy infantry with a few cavalry units for flanking and you'll generally be able to beat opponents unless your generals suck (the quality of your generals matters a lot more in EU:R than in most Paradox games). Horse archers are pretty nice, but they are hard to come by as the Romans. Protect your civilization level, especially in border areas, to make sure you can colonize. I would regularly launch "punitive" expeditions to go out and attack barbarians before they could form doomstacks and wreck my holdings.