The good:
Its still the best all around gun finish.
Its HARD. Actually harder than a Swiss needle file. This hardness increases the service life of the gun and makes it far more resistant to scratches. Most scratches don't penetrate the surface and are only a bright streak where the scratch polished the finish.
Its so thin (usually around 0.0002") so it doesn't interfere with even tightly fitted guns.
The hardness actually improves the trigger pull and smoothness of the action.
It requires less lubication.
Its proof against all solvents and even acids. Most chemicals won't touch it, and those that do are nothing you'll find around most homes.
Its very rust resistant.
Its "slick" so dirt and carbon won't stick to it and its much easier to clean.
Its one of the very few gun finishes that's considered to be a true life-time finish.
Its available in appearance from the original satin pearl-gray, to a brushed stainless steel look, to a mirror polish.
Some platers will even plate the inside of chambers and bores.
The bad:
Its a "white" finish and some people prefer black guns.
Once done, you can't modify or gunsmith the gun without breaking through the finish.
You have to take care about who does the plating. The best companies are people like APW/Cogan, Metaloy, Armaloy, and Ford's.