A lot of people poop on New Super Mario Bros. Wii for not being original enough. Personally, I don't see it. The game looked a lot like its prequel on the DS, but thanks to the four-person simultaneous co-op, it played like no other Mario title before it, or any other 2D platformer for that matter.
The way the game forces players to constantly vie for physical space inspires all kinds of interactions, both in and out of the game. Those dynamics can lead to a lot of interesting relationship moments (including divorce by some reports).
New Super Mario Bros. U has taken that philosophy towards local multiplayer and put it on steroids with Boost Rush mode. These timed, auto-scolling levels fill the screen with enemies and make safe, stable platforms a rarity. With four on-screen characters playing at a time, the pace is hectic, space is limited, and the challenges can feel impossible. That's where the fifth player comes in.
The player utilizing the Wii U GamePad is in an interesting position. While they don't have to worry about maneuvering a character on screen, they do have worry about keeping every other character alive at all times. They have the power to crush enemies and create blocks with the Wii U GamePad's touch screen, and just like Uncle Ben says, with great power comes great responsibility.
That makes for an experience where the players still have to work together at all times. The difference now is that the player using the GamePad is placed in a different, more god-like position. Will they be a skilled, smart deity or a stupid, sloppy omnipresent moron? The answer to that question will determine the fate of the four players trying to survive this onslaught of goofy madness.
It's the kind of game that works as both social lubricant and as a Rorschach test. Inhibitions drop quickly when life or death is determined by how soon you command (or beg) the player with the GamePad to save you from being punctured by a Piranha Plant.
You'll also see how secretly sadistic your friends can be. Sure, they'll claim to have put that block in front of your jump to try to help you, but when they chuckle to themselves as you plummet to your death, it won't take a psych major to pick up on their sadistic streak.
The game offers all new ways to help (or hurt) your friends in a local co-op environment, with the intensity of those interactions exaggerated by the game's fast-paced, tough-as-nails level design. If New Super Mario Bros. Wii was like going on a treacherous hike with your friends, then New Super Mario Bros. U Boost Rush mode is like running a marathon with them through a mine field, while one player looks on from a distance, doing their best (or worst) to digitally defuse the bombs before they blow.
It may not be a reinvention of the 2D Mario series, but stuff like Boost Rush mode shows that Nintendo is still working to find new ways to make local multiplayer feel fresh and exciting.