The farther I get into AoW1 on Normal, the more I find myself having to use exploits and leader assassination. The AI starts with a huge advantage, and even if you roam around razing everything, they don't lose troops due to gold loss to nearly the extent that the player would. High-level hero units in AoW1 are a bit OP, too. Unless I'm missing something, the expand-and-conquer methods unexpectedly stop being viable partway through the campaign. The one thing I've heard about SM is that heroes aren't as OP, so I assume some combination of scenario objectives and empire management will be comparatively stronger.

Maybe more experienced players disagree, but that's how it's been with me. I'm in the light campaign, lizards/highmen route.
Also, I've found SM to be a little harder to deal with interface-wise. The layers of foliage, fog, and the viewing angle make it sometimes hard for me to click on the right unit, or in some cases, even notice that one is standing there. I could probably adapt, but AoW1 is a bit more clean and simple.