Wow! Now that's a crazy way to build a hill, one that I've never seen before as well. The shape is a little bit odd, maybe, but for a new technique it looks great!
It's an interesting hill design, as others have said. I do have one question though, but perhaps it's a bit obvious. Isn't it a bit intensive in how it uses the typical Lego foliage piece? Those are rare enough to me that I'd rather save them for other plants, but to achieve a "swampy" or "thick" vegetative look, I think you've hit on something.
Another round of thank you-s incoming!
Tycho: It indeed uses quite an amount of those, but this particular example was achieved with only 1-2 layers of leaves all around, so I believe it's still possible on a larger scale.