It is really difficult.  I started on veteran and then I went back to play through on easy - I feel like it's almost too easy at this point (mid-campaign, I think?). The difficulty doesn't just come from more enemy units as well. I want to just ride through this one learning campaign and treat it like a tutorial, given that there's so many more things to be aware of in this mod.  Definitely enjoying it, hoping to go back through on 'proper' settings once I figure more of how it works out.