For starters, dont make links to imageshacke when uploading terrains, there is an "Upload Attachment" button under the reply box; use it.
Now, for the terrain:
For some reason I love the look of the river you made before the falls, and then the lake itself looks... Bland comparred. The mountains looks quite unatural, the snow shouldn't go all the way down to the ground, rather have small dots of snow on top of them instead, also; dirt mountains with snow on them seems to be a very... new thing to me, and last time I checked that didn't exist, always think about reality when terraining, it will help you a lot ^^
If I were you I would try to use the rock tiles combined with some Snowy Rocks lowered down into the mountain side to give a nice and snowy look, but still keep it alive. If you dont know how to lower object that is done in the following way:
Select the object, then hold down CTRL and press Pg Dn; Pg Up for raising them
Now, as mentioned your terrain is in DIRE need of more details, think about it; since when were the last time you saw a somewhat lushy (based on the trees and grass) that was as barren as yours? At least add some grass models, grass isn't flat you know ^^
And when it comes to the fog and the sun, it doesn't look too good. The sun is a simple one to solve, simply take the glow model and place it close to the camera so that it covers the sun; this will make for a nice and warming effect and make the light seem like it comes towards you and not just is there, on the horizon. Now, the fog is simple as soon as you get a hold of it, took me some time in the start also. Since you seem to be famillar with how to find it, change it and enable it I wont go through that part, rather write the values you would most probably need;
Z Start: 0. (setting this option to zero will make the fog cover the entire map.)
Z End: 2000/4000 (this is what decides how dense your fog is)
I would also advice you not to use units in terrains, but your Jaina seems to fit; but in most cases units dont fit in with terrains. That, however, is a personal matter
I hope this was of somewhat help ^^