Specifically, it's about the game's difficulty.
Last month, Jorge wrote a thought provoking post about the shortfalls of Donkey Kong Country Returns' cooperative multiplayer. Jorge and I have known each other for a long time, which means we know exactly what to say in order to goad one another into action. Master troll that he is, Jorge suggested that perhaps cooperative multiplayer doesn't belong in 2D sidescrollers, and cited NSMBW as an example of a game that fails because its high difficulty can dishearten less skilled players.
On the subject of difficulty, we are in complete agreement: NSMBW is hard, and things only get trickier when more people are involved. However, I feel that the game's knack for pointing out player inequality isn't a sign of failure, but rather of success.
Like all Super Mario games, NSMBW doesn't coddle its players. The language used to describe its rules, its gameplay systems, and the stated philosophies of its designers make it clear that NSMBW is a game that demands players own up to their mistakes and find ways to either compensate for them or avoid them in the future.
Repeated player failures and punishing difficulty often point to problems with a game's design, but there are games in which these exact features are signs that that the experience is playing out as intended. NSMBW is difficult: it's harsh on mistakes, it can be cruel to new players, and it requires a high level of skill. These truths are not flaws, but strengths; NSMBW is an example of a game that realizes the intent besides its design philosophy. Unfortunately for some, said philosophy can be pretty brutal.