I've been saying it for a while, but I'll say it again. I'm excited about New Super Mario Bros. for the Nintendo DS. Now there's more new information about the game, and from the sounds of things it looks like the development team has taken the best elements from Super Mario Bros., Super Mario World, and Super Mario 64 and combined them with plenty of new material into one grand package. Nintendo veteran Takashi Tezuka has revealed some interesting things.
The gameplay itself has a lot of replay value, I think. In addition, you won't be able to save your progress from level to level; you'll only be able to save when you reach the next world. So in that way, the game system is designed to challenge the player and encourage replay. Also, remember how in Super Mario 64 you needed to collect a certain number of stars to reach the next course? We're doing something similar to that. There are also similarities to Super Mario World in that different branches exist to different levels. By completing some task, you'll open a different branch.
What else is there to say? New Super Mario Bros. releases in North America this May. Personally I think there should be a national holiday declared to celebrate the release, but that means stores would have to be closed and the mail would not be delivered, so we wouldn't actually be able to get the game on the actual holiday itself. Nothing worthwhile is ever easy.