Brilliant, there are some areas you will immediately notice are different when you reach but it adds rather than takes away; while the overall feel & gameplay is the same. Excellently executed dialog too.
Edit: Game isn't optimised for Integrated GPUs, so if its too dark or the flashlight doesn't work, pull up the console (~ key) after activating in options, then enter the following (without quotes)
"mat_hdr_level 2
mat_tonemapping_occlusion_use_stencil 1
mat_dxlevel 98
cl_showfps 1"