- i think the fog colour is fine, its just too strong, should be more like the last pic in ratchets above post

- now that i see it, terrain shader may be fine, may be the tiling is too small though ?

- bad plant textures but i know youre no artist so cant say much

- maybe try to enable decal shadows for everythng? how does that look? hows the fps ?

- hdr tweaks

we're just trying to make it better, not saying you havent done a great job thus far