Good on the surface, but little depth
The battles haven't changed too much, which is good I guess. The interface and controls are essentially the same, and you still have the rock-paper-scissors approach to units. The graphics have definitely improved, with full 3d units instead of sprites like in M:TW. But graphics are only entertaining for a short while, and don't really add to the gameplay value all that much. Eventually you'll find yourself auto-determining battles simply because they aren't fun or exciting enough to spend the time managing.
Rome: Total War is enjoyable at first as you learn the new features, but in terms of actual game play value, it hardly improves at all on the formula used in Medieval: TW, and you'll find yourself getting bored doing the same thing over and over as you play. The complexity of the game makes it hard to become immersed in, and eventually just gets old.