I too think the terrain is DCS is getting a little old. Sure there are some improvements compared to the first Lock On and Flanker, mountains and hills are more detailed and water looks a little better. But the terrain needs to be redesigned eventually.
I think the lightning is pretty good in A-10C. Not as good as it would have been with DX11 though. DX11 allows more colors and better contrast when using HDR - Take a look at DIRT 2 with DX11 - It looks amazing compared to GRID's DX9 graphics.
The models and cockpit in A-10C are truly a work of art. Love the little details such as the spinning GAU-8.
I've only had a few flights in the A-10C and love it so far. I'm sticking to basic flight training for now. I don't have the stomach to dive into all the avionics and manual just yet