Napoleonic armies used a wide variety of formations, and cavalry was still a powerful and vital arm. The engine has been altered to include a large number of formations, and also changed to handle all the details of cavalry charges - charges, continuation charges, and so on are all taken into account. Infantry in line delivers the most firepower, but is terribly vulnerable to cavalry. If the infantry forms square to save itself from enemy cavalry, it is much more vulnerable to artillery, and it becomes nearly stationary. Cavalry is incredibly powerful against unprepared enemies, but fragile, and likely to shatter if the enemy forms squares in time.
Artillery has a long and powerful reach, but is nearly defenseless in melee combat.
The player must juggle all these interactions, using combined arms to defeat the enemy. If they form square, to defend against the cavalry, they are more vulnerable to the infantry. If they form a line, to deal with the infantry, the cavalry may fall upon their flank and rout them. I find the increase in tactical complexity makes the game more interesting than its predecessors in the series, but your mileage will vary in accordance with your tastes. If you prefer the slugging matches of the American Civil War over the fencing finesse of the Napoleonic era, you may not be as intrigued.