Is everyone moving core units to the next DLC or starting from scratch?
I played Panzer General in the good old days and decided to try Panzer Corps and the Campaign Megapack. I haven't been disappointed. I needed a few reruns of the first few scenarios on the default settings to get up to speed and and eventually achieved decisive victories in the '39 campaign. I didn't have a clue how to best handle the naval aspect of the final Narvik scenario and allowed the enemy destroyers to sail right into Narvik causing a bit of chaos on the way (especially when they dropped anchor at bridges). Despite this I destroyed all the enemy capital ships while retaining all of mine (badly mauled).
My core units were adequate for the Narvik campaign but completely useless for carrying over to the first scenario of the '40 campaign (Eben-Emael) and I lacked prestige points to buy more suitable units. Switching to the default units provided by the scenario made a decisive victory possible at the first attempt.
As others have said elsewhere, you really need to build up a good range of reserve units but I was never able to gather enough prestige points to do this. Perhaps I shall do a rerun at some time to see if I can do better but for now I'm working my way through a first attempt at the complete campaign series and am really looking forward to being mangled by the Red Army [:(]