I don't believe you can have a conversation about graphics without including performance in the discussion. Anyone can make a game that looks pretty in screenshots but that frequently falls below 20 fps and suffers from rampant screen tearing and the like, and many developers do in fact make such games.
Part of what makes Mario Kart 8 technically impressive is its locked high frame rate even during 2-player splitscreen, all while the Wii U is wirelessly streaming a video feed to a second screen at a higher refresh rate than many HDTVs.
Anyone who is attempting to argue that Mario Kart 8 is graphically impressive purely on the basis of its character models, textures, and lighting is making a terrible error.
For the sake of simplicity, in this thread:
Graphics: The polygon counts, anti aliasing, anisotropic filtering, shading, shadows, textures and so forth.
Performance: Frame rate, resolution, screen tearing.
Art direction: Kind of speaks for itself.
Something like MK8 excels in performance and art direction, but is lacking graphically. It seems to be the opinion of some Nintendo fans that MK8 is a graphical, performance and artistic power house, which is frankly not true. The limitations of static console hardware essentially means that the developer has to swap between graphics and performance, so believing any game excels in all three is willful ignorance.
Just like how you could say MK8 is lacking graphically, but excels in performance, you could likewise say DC excels graphically, but is lacking in performance. Just pinpointing out nothing can hit the full potential of both ^^ People will then also debate about what balance of the two works best for what types of games, but this isn't the place for that type of discussion.