As far as I am concerned, canikon has never been equal to Minolta glass at given price points until Sony took over. Suddenly, Minolta legacy glass went through the roof.
For example, the 200/2.8 G and the 300/4 G both sold for about $800 new. Both crushed the competition at the time. After Sony took over, they were discontinued and people immediately paid top dollar for the remaining copies.
Also, I have seen several reviews where the 24-70/2.8 SSM ZA has been found to be better than the competition and Michael Hohner's site shows reviews that put the 70-200/2.8 SSM G above the competition.
I have tried the competition. I like the Minolta interface better and I like their glass better. Sony has carried on these traits, and even improved them slightly in some respects.
G lenses should be...
Constant aperture that is relatively fast for the focal length
Top glass with good colors, bokeh and sharpness (and well corrected in the edges)
Built like a tank - mostly metal and rubber with a minimal amount of high quality, rugged plastic (including the sunshade!)
Internal focus and internal zoom (for better weather sealing - like the 70-200/2.8 SSM G)
A 2 year all inclusive warranty