I really like the lush vegetation in the foreground. Nice work!
It's pretty obvious that the quality of the vegetation is due to the high AA settings, always thought that AA @ 10 was sufficient but this looks way better

The background is indeed a bit dull, but that's also because those trees are quite darker compared to your foreground.
The main issue is what cajomi stated, like in TG0.9 it is still very difficult to shade steep slopes and to make them look interesting.
Don't know how to do it but you might try to replace those mountains with other ones using some kind of masking technique.
Maybe loading another heighthfield on top of those mountains and checking "flatten terrain first" will do the magic, only thing is that the edge of the loaded terrain should have something interesting

The plain soft atmo is a good choice and I'm happy you didn't add a moon

Looking forward to see it updated

Martin