It makes it ridiculously better. The diplomacy, the mix of units in each stack. You should see the number of additional units in this mod. Basically every distinct regiment that existed during this time is in. The AI uses naval invasions much better. You play on hard now and you will have to have game to pull out a victory.
The only thing I do is houserule out my own forts by destroying the walls of any city I own because they are too easy to defend.
Even if you only play the campaign, its very good.