3 Items
(1 silly perhaps)
from 
Elemental Forums
Elemental Forums
Not sure of costs as haven't played much Empire yet, but. And yes Balance is forthcoming, I know. Just saying... 
1) Sions, or any enemy with, with Critical Strike are brutal. Seeing 3X ATT strikes with 27ATT points on a single unit. (A single 71HP strike kills all but the most sturdy)
2) Lord Hammers appear quite early. Same issue.
(silly one perhaps)
3) How do you end a Siege? Sieged a Town, then took it over and the Sieging unit (Hero) would not move again until, as the pop-up stated, I ended the Siege.
Never did find the End Siege button?