I spent a few hours having a go at creating a map. Its really not as easy as you'd think. Its like firing up paint and trying to create a masterpiece
Theres a few things which are a lot harder than they should be, its pretty much impossible to do small rivers as the smallest brush size is still pretty big and it wont do small sharp drops. You could do a huge rock-face 100 high, but at 10-20 the game insists on smoothing the corners out, so best case scenario you get a 45 degree angle, but to have flowing water it needs to be reasonably deep, which means it has to be fairly wide due to the 45 degree aspect. Instead of what should be a stream, you've got a decent river.
It might not help that ive designed my map to be sloped to the sea. Its not a heavy slope, but i suspect it encourages the water to rush and slop over the edges, which results in taller banking. I dont think the water simulation in the editor is quite the same as in-game too, its much faster and manipulating land near water causes tsunami's! So its very finicky.
The 2 biggest things ive discovered from it all is that
A) Build everything right hand drive! The game automatically flips the road directions for LHD, so if you put in highways for LHD all the assets (junctions/interchanges etc) are RHD.
B) Its so so easy to get lost in the scale of building a map. The only thing which really brings you back to scale is dumping down a few trees. Its so easy to forget your working on a map about 49 tiles in size (7x7, 5x5 playable with 1 all the way around) and you end up working on something which seems correct for 1 tile, but its huge and so are all the rivers, lakes & mountains etc.
I've only really spent time in the top left corner, 90% of which is outside of the far boundaries

I can see it being something that takes quite a long time to make something with a little character.