I still can't understand why the Creative Assembly leaves it up to the modding-community to make their Total War-games into what they are supposed to be. Whenever a new game hits the shelves, leave it there for six months and only then pick it up. By then many a few great mod(-dification)s can be found which improve the game beyond anything CA released. Enhanced gaming experience ahead!
The performance of both Empire and Napoleon isn't all that good, sudden lag is quite normal if you have anything but a brand-new, state-of-the-art gaming-rig. The engine renders in a completely wrong way, or so I was told. My brains stop working when something becomes technical so don't ask me how and why. What I know is my perfectly suitable machine wasn't able to run bot Empire and Napoleon properly without the GFX-card making an awful rattle.
Now some chaps: Brigadier Graham and Killzone, performed miracles and found a way to let the engine render battles far more efficient. The results: better FPS, better quality and better overall performance of the game. Why can't SEGA do this themselves you wonder?
Next I focused on the looks. Well, the Total War games have always been about looks and mostly anything else comes second. Even so, there is room for improvement in this department as well. The smoke from musket and cannon discharges disperse quickly and the explosions are unimaginative. Enter the to Smoke and Blood mod. (the second part is a little bonus) and you have all the "atmosphere" you want. Clouds of smoke linger for minutes, explosions are great and with one of the good sound-mods (I used the Ultimate Sound mod) the noise is realistic as well.
So, we have a better performing, better looking and better sounding game, we now can actually feel like we are part of the battle and commands amidst the chaos. The original units however, are a bit bland and almost color-coded. In comes the modding-community yet again, with a large selection of new units/skins. In general they are more detailed, better researched and thus more realistic then the original units as well.
There are scores of different unit-packs as well as completely overhaul mods which incorporate many more aspects of the game. The one I prefer is Georider's. A total of 88 new units more then doubles the vanilla number of units.Whichever faction you will play you will find something of your liking.
To complement this set of fine mods there are some smaller ones which might add some extra depth: Longer battles, Massed fire, Larger units and Tighter formations. You choose which you like and get the game you want, or hoped it was in the first place. The preceding was just a list of my favorites and most certainly you will find even better mods when you look around on this and other sites. The search is well worth it so, good luck!
Finally there is the main problem with every release, the AI. Empire: Total War excels in this case, it was abysmal. In Napoleon it is so-so. Mods slightly improved on the AI in Empire and in Napoleon they do yet again. Luckily CA has put in some effort and now the AI is something you can live with even though it isn't as good as you wish. There are some mods which enhance the battle and campaign AI but it is all a bit iffy as no one knows exactly how the AI works and how to edit it. Let's hope the Shoguns will know how to fight when we meet them on the field of battle in 2011.