I'd say that Rome gets a worse rap than it deserves. The traits do have a bit more synergy than I think most people assume. Commercial means that Rome has more shields (due to lower corruption) for making units, and more gold to support a large army. Militaristic is the perfect trait for expanding your empire over large spaces through military force, which works well with commercial, making conquered cities over a large space more productive. Rome isn't the best warmonger or peaceful builder, but it's certainly one of the better civs, IMHO, for fighting, and can generally enter into extended periods of peaceful building. This duality is partially possible due to the awesome Roman UU, the Legionary, which are both great defenders and respectable attackers, in both the ancient and middle ages.
Rome's real problem is that it's not any good in the early expansion phase of the game. I have yet to play a game with Rome in which I didn't have to start an early war to gain some space for my empire (I generally play huge pangea maps with 80% water on monarch level, with eight-twelve opponents). Unfortunately, this means that Rome is often lacking in culture in the early game, gets a golden age often before monarchy / republic, and is behind in techs. If you can survive the early stages of the game, however, I've found Rome to be a respectable civ.