Some people say there isn't a big difference between DX11 and DX9 well that's because DX9 was the biggest step forward in PC graphics hisotry, after DX9 we are touching up elaborating and perfecting. i.e. Shadows, lighting/shading etc. which aren't elements of graphics that need a lot of work post DX9. If you're actually playing in DX11 vs. DX9 the difference can't be noticed in a screenshot it's difference is noticed when objects are moving around the environment. When you can see the light reflections, and the shadows moving, tesselation, and shading design improvments.
The reason some people think that there isn't a big difference between DX11 and DX9 is because in DX9 the graphics are all there they work most everything can be done in DX9 but MORE can be done in DX11 like I said elaborating and perfecting.
DiRT 2 isn't worth playing in DirectX9 the gameplay isn't that great of a step forward but the graphics technology is.
I am looking for opinions or knowledge about this matter or any comments.
I won't go into too much details but I believe the biggest leap forward with DX11 is the Tessellation feature...at least visually. They also took a huge leap in the multi-threading but you won't see a graphically improvement on this.
Google Tessellation and look at DX9 or DX10 Images vs DX 11 Images.
Nvidia and Microsoft have great videos (Demos) that explain what Tessellation does.
Tesselation is the only real major graphical upgrade since a lot of the DX8/DX9 stuff was added to the API. Even then, it takes a LOT of horsepower to use on a large scale, so its often unused.
Again, Rasterization has gone about as far as it possibly can. The next graphical improvement will be via some form of Ray Tracing. I simply can not see getting anything else graphically out of the existing API. [Hence why most of DX10/DX11 has been improvements on the speed side, rather then new graphical features]
Tesselation, to me I don't know if everyone has worked on this or looked at this but there are specific algorithms in which your eye and a picture or a computer renders depth perception, and in DirectX11 we are one big step closer to having a perfect vertual representation of depth how far an item is away from apearing on the screen. Displacement maping is incredible means for using shading on a texture to tesselate a 3D object. Smooth Shadows AWESOME! although not put in to full effect even in BFBC2 (+) should though. But not And Yes Tesselation makes things look smoother a major step forward, I think that the huge step forward is the actual API (Aplication Programming Interface) Meaning the code is easier to work with deeper code. Perfect Depth Perception Is apparently really difficult to reproduce but DX11 is only a minutia away. Tesselation will be exploited and hopfully smooth shadows will because you don't have to have anything else but smooth shadows and it looks two fold better.
-32X AA (is actually very nice you might not think it even improves over say 16XQ to your naked eye amazingly enough)
-API In General I'm Sure?