Very good ideas Ares. But with your maps, I notice the flat plane effect. Everything seems to be on it's own height, and there's really no up/down hill effects. It's not incorrect to do it this way, but I think your maps will look a little better with the suggested changes:
I love the underpass thing, but it's just too short. You'd have to make a crawling sprite to make it believable. Another thing that bothers me is the tree stump, cleanly cut. If I were a logger, I definitely would not cut just that one tree, especially because of it's positioning on the hill. I recommend that you just put a normal pine tree there, like you did on the hill above it.
The huge cave opening used as a waterfall doesn't really please my eye. Mostly because the edges are too round. I think if you can edit in stalactites, and roughen up the edges of it a bit, it would work better. Also, the two holes at different heights, both pouring water is a bit confusing to me. The smaller hole I like the best, but I recommend you edit the hole opening to make it even smaller. Also include a few cracks on the walls, with rocks & debris on the ground, or in the water, below.
On this map I think you just need to play around with creating the illusion of going up and down hill. You should use different height walls, and move the poles a bit closer to the edge.
Overall, you did a good job. I think your maps are really creative. I would just suggest that you work on smoothing out the edges of the walls, to make them seem less square, and use some lighting effects.
edit: :crazy: I thought I was going to be first to post! Looks like twelvestarfish13 beat me to it :huh: