Mike Rundle:

Designs can succeed or fail on a number of levels, some of which are subjective, some of which aren’t. Things like the overall concept, mood and its visual appeal are subjective: one person might think a design succeeded in its overall goals whereas another might think it failed.

So without any context what can you really critique? Design execution. The execution of a design is the nitty-gritty details of the design. The pixel-level details. The alignment of individual elements. The kerning of a logo or headline. The sharpness of an edge. These can be wrong. These can be so incredibly wrong that they stand out no matter how good the overall concept, mood and visual appeal may be. Screwing up the execution of a design ruins the design. Game over, it’s wrong, and no context is needed to understand its wrongness. A 400×300 pixel screenshot on Dribbble can be wrong without knowing anything about the project. An iPhone app icon can go from right to wrong in just a few pixels. One misplaced pixel. One misaligned button. One blurry edge. This is what makes a design wrong, this is what makes an execution of a design go from good to garbage.