This is excellent. If you don’t buy it, you need a kick in the teeth.
It got very hard towards the end of the Aztec campaign, with one level in particular seemingly at stalemate for 20 minutes whilst both side just spammed units, until I decided this was never going to work and gave up. Next go seemed much easier, although I did finish the first objective much more quickly.
Now, I’m onto the second level of the Chinese (or Asian, depending which part of the screen you read) campaign. Looks like it’s going to be hard again as my units seem somewhat feeble.