Hopefully this is just work in progress and far from the end result.
The bumpmaps look horrible, especially with the current state of LOD.
The lighting is wrong, way to saturated.
The sun might look yellow/orange, but it dosn't change the material of things, so please tone down the color saturation on the lightsource.
Also, the shadows are way to pronounced, rarely if ever do you get hard-line shadows from sunlight, so some scattering of the shadows would be good!
Truthfully, as it stands right now, I would say Ogre was way superior.
And just throwing automaticly generated bumpmaps onto something really dosnt make it look better unless its done right, and done so with intent from the very beginning.
Clearly the textures in AO is made without any such intent.
They probably cheated in bumpmaps without actually having them, adding depth with artistic eyes instead. Cheating is considered a good thing as it reduces resourcedrain, thats good.
Infact thats exactly what bumpmaps are, cheats to add geometry. But seeing as AO's textures are allready cheated to add depth with color information.... To create a good bumpmap you need to create a high-poly version of the current geometry. This would require a COMPLETE workover of EVERY single rock and surface in AO.
I would recommend strongly against adding bumpmaps on the current ground textures in AO seeing as all it would accomplish would be making it look like plastic.
I think ive said this before, but ill repeat myself. DirectX is just not as good as OpenGL, it's merely easier, and you will pay dearly for being lazy with the quality of the end-result.
If nothing else, _PLEASE_ scale down the value of the bumpmaps by at least 0.5 and remove specularity from them.
I do hope I will be proven wrong.