The principles of formation warfare are not exactly rocket science. Anyone with a decent idea about military tactics will soon grasp all the basic principles of using cavalry, infantry and artillery. Obviously with experience comes best practice.
However, for those of us who have that base understanding and are well versed in our own strategies and ideas of how our own battles should be fought, the challenge becomes routine and therefore no longer a challenge.
That is why having large numbers of units makes for an interesting and more challenging game. When you make a mistake with large numbers of units, your mistakes are more profound. It is also much more difficult to manage a large number of men, something every past general has to deal with. Thus the inherent challenge of having good situation awareness and knowing where your men are at anyone time is stretched to the limits by having greater numbers.
Additionally, as implied from the above posts and by Darth, this is the Total War series. This the the series of game that has a profoundly unique appeal. This has been one of the best series ever made. Personally, I do not enjoy these silly "real time strategies" that involve a few units of men in a so called battle. The abstraction is too obvious for someone like me. A great majority of RTS are mere graphical revisions of the Command & Conquer forumla of "strategy" game. However, everyone knows each "battle" in a C&C-esque game is a mere stepping stone whereas battles in Total War have always meant something. Total War has always been about big (meaningful) battles with lots of soldiers fighting. Regimental combat rather than unit to unit combat (a mere poor abstraction in other games).
Lastly, I really do see Total War as more of a simulation than game. A historical simulator. Believe it or not, before I played Empire I had an idiots understanding of 17th and 18th century warfare, but playing it has prompted me to read up about it in my own time. Total War games are of course also a thinkers series. You really have to have the brains to do what you need to do. It is definitely not a point a click graphics show.
That said, numbers IS the thing that is most neglected by developers these days. The vanity drive for graphics kills many games with great potential. Here, as Total War fans, I'm sure we want more epic, more interesting, more challenging battles rather than another graphics showcase.
I do not want to feel I'm doing border skirmishes all the time. There are Friday pub brawls where I live that are more epic than vanilla Ultra size setting battles.
If I really wanted nice things to look at, I've got plenty of other places (and people
) I can stare at. When I play a game, I want a challenge and to feel immersed. Every Total War battle should look like the Battle of Pelennor Fields in Lord of the Rings: Return of the King. Having 80 poncy cavalry just looks stupid.
That is why I think this mod and the potential of the engine is a godsend (if they can optimise it more and fix the damn bugs!!). Well done again Darth, and shame on you if you do not believe in epic battles.