The terrain looks awful in my opinion. As you can see on the picture, he got some spots which is repeated. Looks stuff.

And I also agree with Conan, that the boundaries is too sharp. The boundaries should be built as terrain too, but more sharpness, if you don't want people to "escape".
The hardest part will be adding grass to it.
And why is that the hardest part? It's the only part when you don't have to be creative, just plant grass on every naked spot.
If you've done the cubescaping correctly you should only use the plates.. : 32x32, (if you got such big spot) 16x32, 16x16, 8x16, 8x8, 4x16, 4x12, 4x8 and 4x4. Just a tip