New Super Mario Bros. Wiiseems like such a simple thing -- more Mario platforming, with some multiplayer this time, but the simple fact of more Mario platforming is almost intolerably wonderful. Maybe it's because we're super-tired from E3, but just look at the footage. Look at the adorable propeller suit. Look at that cloud enemy. The giant, friendly air manta rays. There's all kinds of crazy new Mario stuff happening, even without the multiplayer.
The trailer shows the game's casual mix of coop and competitive gameplay -- sure, you can jump on each other's heads and stuff, but Luigi is also seen carrying Mario around on some moving platforms.