I will expand a bit on why Inferno is "easier" (in a playability way) than Nevsky.
In Nevsky, moving an army is hard. You can move via waterways or roads, and you have to have boats and carts for both of them. Except in the winter, when you have to have sleds. Figuring out how to keep your army fully provisioned and moving, on different types of ways, and in different seasons, is quite the challenge. Poor planning (and inexperience) in Nevsky can be challenging.
In Inferno, the Tuscan infrastructure is more developed and doesn't have problems with winter weather. There are highways (I forget the exact nomenclature) that allow you to move further and easier. It's really easier to raise and move an army, so you can focus your energy more on fighting the enemy than just fighting the elements.
Inferno does add one new feature: Revolts. They are mechanically easy to resolve and add a new strategic element to the game, but they don't make the game itself more complex.
Now it's off to Rally the Troops, where I think I have a couple of Nevsky turns waiting for me...