These are very different games. The short campaigns will feel very much the same, there are not as many scenarios in WON, but the ones presented are nice.
A major difference is the Grand Campaign. If I were summing this us across what I think are the community comments, I would say that if you enjoy pbem play you will love this game. It has levels of complexity in unit building, national development and diplomacy unlike any other Napoleonic Grand Campaign game. With seven players this game is very enjoyable and challenging.
Also, if you like to play solitaire against yourself, as I do, it is the best Napoleon era game available. While Victory and Glory is a fine game, you can only play as Napoleon. If you look forward to exploring each faction by playing all, this is a great option.
It seems players who only like playing one nation against AI are not happy with this game. This is likely because it is so complex it is hard to model excellent diplomacy and combat across so many dimensions.
The new engine is very worth learning. The newer game plays so much better.
Incidentally, if you do not have NCP, the Peninsular War Scenario is spectacular. Might be worth buying just for that play.