Shepards Dog: One thing I found about land combat with Empire is that compared to previous version of "Total War" it is prudent to assign orders to your units and then
don't micro-manage them. Let them carry on as they've been 'trained', reissuing orders only when necessary.
There were AI problems in the beginning but the blunt mistakes have been fixed. However it's not easy to get AI to be as smart as another human most times.
All in all playing Hard/hard I still won campaigns (England and Prussia) only in the last 10-15 turns (out of 200). Considering that any time I started a campaign, realized by turn 20-30 that I screwed up my strategy and quit would technically count as a loss for me and a win for the computer, it's really a pretty challenging game from that standpoint.
PS: If you ever wanna try a land battle online with someone who has experience but still kinda sucks, I'm your guy