With Napoleonics it is important to decide what level of game you want to play before deciding on the rules.
If you want to fight Borodino, Waterloo or Wagram and such battles in their entirety Black Powder will not work. For that you need to look at rules like Grande Armee, Blucher or (my favourite) Volley & Bayonet. These use bases as brigades and you game with multiple Corps per side. Things like formation changes and skirmishers are abstracted out to concentrate on massed units.
If you want smaller battles or to play only part of a major battle with game options for showing formation changes, skirmish screens etc but still have aspects of higher command then Black Powder is OK, but games like Republique or Lasalle have much better flavour.
Going down to a lower level again with only a Division per side you can have a lot more detail of the units, formations with rules like General de Brigade or Rank & File.
There is an excellent comparison of many different Napoleonic rules here:
http://www.deepfriedhappymice.com/html/rd_napoleonic.htmlI have only mentioned above the ones I actually play.
Really comes down to how much time and how many figures you want to spend. To some extent most rules are scaleable (or so the authors always claim) but there are such good sets written specifically for the different scales of game that making something not designed "fit" is never going to be as good.