In attempt to classify lenses word sharpness is the most frequent, meaning very sharp lens is very good lens. Even and Zeiss advertise their ZF lenses, beside high resolution slogan, as "sharpest lenses ..." so it turns that lens vague term "sharpness" is to many the most important think in classifying lenses. "Good lens" to me means a lens that consistently producing an image that coincides with my photographic requirement. As photographic requirement (standard) are different to different people, so and the same lens can be good to one and not good to another. In that way and Leica is not the best manufacturer of photo lenses, but just a manufacturer among other. What GOOD LENS means to you?