Win10 64 bit; 24 gigs RAM; third-gen i7 CPU; AMD 7xxx GPU (Crimson ReLive drivers)
Broken: hash 6cd1d34
Short description of error
When using a low neighbor weighting value like 0.2 (the second of the two feature weight fields), the denoising algorithm used by Cycles will appear to leave a lot of pixels unprocessed or only partially-processed (creating something akin to .jpeg compression artifacts). I don't know if you will tell me to just leave the fields at their default values, but many scenes require a low value for the second one or otherwise a lot of edges and small details will get blurred over (especially details that are only visible through reflections and glass and especially any details in more dimly lit areas).
Exact steps for others to reproduce the error
Open the .blend file and render the scene.