Large playable landscapes

Hey guys! I'm currently working on a roughly 3kmx3km forest landscape for a game and I have some questions for those that are more experienced at working with natural environments.

My first approach was to generate the terrain in World Machine, I ended up with a really nice looking terrain, but after actually running around it in the engine it seemed a bit difficult/annoying/dull to navigate around mainly due to it being very "slopey", it also seemed like it would be tricky to place trees or architecture because of the slopes. Then I tried hand sculpting a bunch of crags on the slopes, which made navigating around a little more friendly, but it ended up looking odd and unnatural, and running that hand sculpted heightmap through World Machine to add erosion turned the crags into slopes again.

So my question to anyone who's worked on large landscapes that are playable, am I doing it wrong or are the landscapes just supposed to be like that? What is the best approach to have it look natural and still be playable?

 

You have to post a screenshot to understand the problem better. Which resolution does your terrain (heightmap) have?