Like any game FW has its little quirks and oddities, but the thing that makes it great to us is the focus on command and control. In many wargame systems you'll find yourself poring over your army's movements and tactics. You have a godlike level of control over each of your little figures, only losing your ability to determine their every move when an unusual psychological effect afflicts them.
FW takes a different approach, placing you much more in the position of an overall commander, issuing orders to your commanders and struggling to match their reactions to the battlefield situation. What is more you need a physical (or metaphysical) means of conveying these orders- if you can't get a messenger through to your men you might even have to send your warchief after them yourself!
On top of this you have the problem of ill-disciplined troops failing to respond to your orders, and even suffering from ongoing psychological effects, like 'bloodlust' which causes them to go charging into the nearest enemy, and probably getting minced in the process...