I am currently learning it. I made a sort of EVA "simulator" where you can fly around the Discovery Space Shuttle, over the Earth. Now the Earth looks like crap and the "fly mode" is very rough ...
Now, the terrain maker is not really bad, but unless you want to sculpt you better make a heightmap using a specialized software (I own World Machine 2, which is really great and let you have big freedom on the terrain generation).