If you enjoyed the original Super Mario Bros. for NES, or the New Super Mario Bros. for DS, you should like this game. This game has *most* of the quialities of a good game: Awesome local multiplayer/co-op; graphics that are awesome; it pays homage to a classic 8-bit game; and it features excellent controls and new features. The only thing that really killed this game is no Wi-Fi multiplayer. No Wi-Fi at all! None. Pfft, thanks alot Nintendo..
But, seriously, this game gets a 8.5 out of 10, and is a must-buy for Wii players.
World 9: After you beat New Super Mario Bros. Wii's 8th world, in the ending animation with*SPOILER ALERT!!* Peach and Mario in a hot-air balloon, Peach will say "Did I ever tell you about the secret world?". She is reffering to World 9. World 9 only has 8 levels that are unlock by collecting all of the Star Coins in each world, and the levels go in order of the worlds. Collect all of World 1's coins, you'll unlock level 1 of World 9. Collect all of World 4's coins, and you'll unlock level 4 of World 9. It just goes like that.
World 1 warp cannon: First, go to World 1-3. Play through the level like you normally would, but make sure you keep a Yoshi. Just before the end of the level, there is a small ledge only accessable by Yoshi. The wall next to this ledge is a pseudo-wall. Inside is a bunch of coins. But this isn't what you want. Stay on the ledge, but don't go into the fake wall. Jump once with Yoshi, then hold the jump button until Yoshi starts kicking and hovering. Push right at the same time. If you did it right, you will go above the level. Keep following the path right above the wall until you come to a warp pipe (You won't be able to see it). You will go inside and come to a room with a red flag. Lower the flag like normal and you will be on your way to the warp cannon.