So far it was possible to win all battles on the normal difficulty. I think people who find it too hard have fallen into one of the many traps (for example Army Organization too low).
This seems to be the problem, the game is absolutely winnable but tuned for people who realize in their first playthrough what you have to do. For example your brigades can be 1500, 2000 or 2500 sized, and this can be decisive.
You also need to know in advance how much supply you need .. how it works even.
Shiloh. It began with a very fun dawn attack on the resting bluecoats.
I didn't like too much how they split up the battlefield into phases and locked most of the map, then switching in the middle of the battle.
I had also held back an entire division because I expected I could send those reinforcements later on but nada. That seems to be another problem - you dont know how many units you can send to the battle. The display before the battle is more than confusing (it said 20 brigades allowed, I had only 12, but it did not say that they all have to be in one Corps)
After the center broke through and crushed the hornets nest (above) the battle transposed into a constant race, and since you cannot make your men run the whole time I just couldn't advance as fast as Union retreated. Sounds stupid but the battle is set up like that, I see no way how you can arrive at the final objective without your men being completely finished at the end.
There was another problem that single brigades of the union routed and then broke through my lines and stayed way back. I could not afford to attack them for the remainder of the battle. In fact they engaged in a long range duel with my artillery which was amusing. I guess it's kind of realistic that certain units would be cut off and under some circumstances attack from the rear. Although there were ~5,000 men in my rear at the end, they did not influence the battle and basically just tied down my artillery.
Towards the end there was this large amount of blue units compressed on the map border, and ready to attack. In the end it was just about looking at the clock and this is the part that I dont like too much.
Anyway, did it and Shiloh was a success. There are still mamy things that one would wish to be improved.