Empire minus scale, plus general badass-ness.
I haven't played Napoleon for very long, but the first thing I was hit by was the sense of purpose that this game seems to put across. You actually have missions and a sense of immersive role-play now instead of the STEAMROLL THE WORLD FLAT vague direction of before. CA have also managed to balance more gripping graphics features (like the muzzle flashes and camera shakes when cannons fire) with superior performance (I can run everything on full now, whereas Empire was on Low and still stumbling) - presumably because there isn't all the baggage of three theatres of war.
The campaign map is a great improvement. The introduction of attrition in harsh conditions adds a real sense of depth to managing the logistics of units, and the new replenishment system that builds up diminished units is a really convenient feature. Plus, the subtle little weather effects and environmental touches really make it feel more alive. You couldn't get this detail on a map like Empire's, which implied for the most part that there was only one notable city in each country.
About the battles, they are, in a word - epic. I was stunned this time about how infantry actually FIRE now, as opposed to making sure that they were all in a perfect line and that their tunics were all immaculate before they thought about firing a shot somewhere in the vicinity of the enemy. Battles are much busier, the constant barrage of gunfire from asynchronous firing is exciting to say the least, artillery actually does something, and the AI is far superior; the enemy can now be arsed to move from their starting position and actually try to flank you and assess weak points in your formations. Smart stuff. It seems CA listened to the community and turned the switch from "Being in a firing squad" to "Oh yes, it's a battle" in terms of the motivation of the computer forces.
Naturally, there are slight holes. The AI isn't impeccable, diplomacy isn't quite there, and to be honest I would have liked a little more freedom on the Grand Campaign equivalent. You only get four factions, and it's basically everyone VS France - but I'm sure modders will make an all faction unlocker pretty promptly like they did for Empire.
Overall, Napoleon is better than Empire and its predecessors. Fundamentally it is smarter, with better graphics, better immersion, and an actual sense of direction. This is a good formula, my only criticism is that "taking over Europe" has been done so many times before, perhaps the next iteration of the TW series could focus on the colonisation of Africa, or something relatively unmolested by strategy titles to date.
It's good stuff. :)