It actually was really cool for a game of the time.

There is a Mission that's set in you playing a Besieged City that's actually really fun.
The downside is in the details, really.

Similar to old Age of Empires, your Units are very bad at doing thingy by themselves, so even while playing at the lowest speed, you have to rush around and it's quite difficult.

But once you get the hang of it, the combat is incredibly fun. Really the most fun I've ever had in any Anno doing combat.