Empire had a rough release, but after many patches it is possibly my favourite of the series!
The campaign map in Empire is by far the best of the series. There are 3 different landmasses (NA, Europe, India) which can be fought over for control, and they are connected by ocean passages. These ocean passages themselves are minimaps with anchors that can be fought over with ships the same way provinces can be. These represent trade hubs, and by docking tradeships you can get additional income. These changes have made the 'board game' aspect of the series so much more enjoyable, and has helped the endgame feel like less of a drag.
There is also research through 'gentleman' units and universities, which can increase philosophy ($$), naval, and land abilities. This adds another incentive to capture and hold huge cities, because more universities means that you can research more tech at once.
Also some factions have elections which are mandatory. There are about 5 seats, and each politician has traits which affect all the different stats, such as morale, suppression, discounts on troops, etc. If a strong party loses an election, it can be devastating for an economy, and can lead to mass rioting.
The actual battles are quite different, because now the main infantry will stand in lines in order to exchange fire. It takes a bit of getting used to, but it is not a deal breaker.
I would advise picking up the Empire/Napoleon bundle on Steam for $30, which goes on sale periodically for $7.50. It's a steal, and is better than buying separately because it includes all of the DLC for both games.