I hear alot about Tessellation but dont forget Compute Shaders are arguably just as game changing. Allowing simulations, AI, ray tracing effects,physics a way to be processed on the shaders of a GPU. We could do this before with DX10 through the geometery shader but it was very very slow. Now DX11 has compute shaders which gives us a uniform (ati+Nvidia) route to run that code much faster. Its by FAR easier from a development stand point and the compute shader pipeline is very fast and efficient. So with that things like physics, water simulation,god rays,Ambient Occlusion, hundreds of light sources, AI and far more advanced post processing effects are possible.

Some games that have effectively used the compute shader:
Dirt 2 (used it for about 2x the light sources of the console version. Relfections, shadows cast, from double the light sources was done mainly on the compute shader. DX9 version does not have this)
Lost Planet 2 (DX11 version has water simulation, walking through it the water in 3d reacts to walking or shooting it. Actual splashes not just a 2d flat shader.)
STALKER: COP (has AO in both DX10 and DX11. A higher quality version of AO is in the DX11 version and runs much faster than the DX10 versions due to being on compute shader)

So not only does it give us more quality. But some games like stalker actually run faster too. Its pretty easy to implement too. Both Dirt 2 and LP2 are on consoles as well as PC.