Uhm, its like blatantly obvious that the main difference is that the dx9 renderer has a more complex full screen specular effect on top.
You get a similar difference in Halo between use20 and use11.
In the 2 version, you get bump, reflection, specular & optionally torch.
In the 1.1 version you only get reflection & specular or bump & torch.
Further, the specular at least is better (ie smoother) in 2 than 1.1.
DX8 looks much more detailed. The tiles image gives you illusion like each tile is casting its own edge shadow,bumps are also a bit more intensive.
Second one is like DX7 render compared with DX8 pixel shaded surface.
DX9 looks like s**t. Even BloodRayne's engine had better stone surface bumps and it was build on top of DX8 technology Source "Crap" Engine haha No,really,BloodRayne engine (really old in these days) impressed me more in some scenes then Source Engine.
To me, the DX9 version look a little blurry - maybe done for speed but I think they need to work on the quality of images. Is possibiable because of soem optimizations that they are doing for DX9 cards. Only a guess.
What would be really interesting is to see differences on latest generation cards like X800 and 6800's.