Use fog! Seriously, it can make your terrain look a lot better if used well.
I wouldn't use those dark green bushes, they don't look good IMO. The terrain is too green, even for a forest. Try to get another color in your terrain, yellow would probably fit well to that Sunken Ruins dirt path.
And it needs more tile variation, especially the hills in the background.
The sun could be a bit orange/red. The gras is too green compared to the red ground. Since the gras is well placed you don't need to add many doodads anymore IMO. Just get something else besides the gras, maybe a cactus or two?
It's also too bright for a sunset.
Since you use the Generic Sky you could do a little trick. The Generic Sky is affected by lights, so you can change the day time to night (or dawn) and then use a light model (I think there's one in the Ultimate Terraining Map) to brighten up the sky around the sun. That gives a more realistic feeling.
I think I have an example laying around somewhere...
Notice how the sky around the sun is brighter than the rest of the sky.