My wife bought me this for my birthday last month. It's awesome! It's a lot like SNES Super Mario World. The multiplayer function is awesome, but can be frustrating, too. Cooperation is a must. I've played through all the worlds (8 is a bitch!) and beat the game, but now I'm working on going back to get all the star coins to unlock the world 9 levels.
My wife and I found an awesome way to rack up multiple 1-ups. In world 1-3, grab Yoshi and head towards the end of the level without killing anything. There's a fire-spitting flower in a pipe near the end. Either eat it or eat one of its fireballs, then head back to the beginning of the level (again, without killing anything). When you're back at the beginning, face right, then spit out the fireball and follow it back to where the flower was and a little beyond. (Don't worry about running into the fireball -- it can't hurt you.) You will rack up a huge amount of 1-ups. If you want to get really greedy, jump down a pipe and when you go back up, all the enemies will be restored and you can do the trick again. (My wife contributed that part.) How cool is that? My kids even know how to do this one now!