I'd say the biggest problem with this terrain is that you don't have a mid section of vegetation. It's either very high trees, or very low gras. It doesn't feel right. Also, I agree with Oziris about the light. You should make the glows come between two trees, not behind one. The big tree in the middle catches the eye, but it isn't particularly nice to look at. Try making an empy spot on the ground will lotsa detailed vegetation that catches the eye instead, if you know what I mean? The upper right corner of the picture looks really awesome and swampish though!