do what cat says. You need more depth. That's what's trolling you. You treat stuff that's right in front of the camera the same way you treat things that are far off. This is a no-no. Add some distance fog to layer it up!
Also I'd definitely recommend adding shadows. You could have a nice shaft of sunlight come down right on the bridge to create a nice simple focal point in the middle. Sorta like this, but not as crummy:

You wouldn't need to have all the shades I have in there. If you for some goofy reason need to keep it at a smaller palette, just chose one color for light and one for shadow. (for each material that is.) (ofc you'd have to blend them a smidgen in the distance to create fog though..)
Also I'd definitely recommend adding shadows. You could have a nice shaft of sunlight come down right on the bridge to create a nice simple focal point in the middle. Sorta like this, but not as crummy:

You wouldn't need to have all the shades I have in there. If you for some goofy reason need to keep it at a smaller palette, just chose one color for light and one for shadow. (for each material that is.) (ofc you'd have to blend them a smidgen in the distance to create fog though..)