While the chaotic nature of the gameplay was a bit off-putting at first, we quickly found ourselves wall-jumping to one of our partners' heads, bouncing along to stomp goombas (among other nasty beasts). Truth be told, the controls for New Super Mario Bros. Wii are akin to riding a bike. We were instructed to hold the Wiimote sideways, a la the classic NES controller, and instantly pushed in the one button and held it, as to focus little Toad (our character) on speed.
The first change we noticed came in the addition of motion controls, where we shook the Wiimote (with vigor) to pick up one of our partners. We could see the game employing this technique for interesting, co-op-required gameplay, though we're less than confident such an idea will make it into the game.
Furthermore, the lack of inclusion of online co-op will be forcing us to sit in the same room as other human beings and that, frankly, is worrisome. But seriously, if Nintendo can make an at least semi-successful online mode for Super Smash Bros. Brawl, what's stopping them from adding online co-op to New Super Mario Bros. Wii?