Well it's not really ludicrous since you need to manage your finances, properties and kingdom. Some mods really expand the features allowing for building, purchasing of fiefs, and fitting out custom armies.
It is not officially categorized as an Empire Building game, so it's not something I would strongly argue over, but it has enough elements from those games to feel similar to me and others might not have had a chance to play the game yet, so get Mount & Blade Warband on GOG!
Im sorry, but wasn't the question "greatest/favourite empire building game"?
Doesn't really make sense to mention a game whereas the empire building makes up for less then 25% of the game, i mean im note mentioning "dynasty warriors empires" here, because in the end of the day, the thing you do most in the game is run around with a unrealisticly large weapon and cut&slash 100s of foes.
Oh it's a bit more than 25% in M&B. Dynasty Warriors is a Hack n' Slash with very small managing features, M&B can't really be played by ignoring the managing side of things. You need to feed your army, earn the money to pay for their salaries; to do this you get involved in trade,property, labor, slavery, politics, and war.
It's all very organic too, like older PC strategy series. It plays like a fleshed out Total War game for me, especially with good mods like Brytenwalda.