The Mario franchise is a great thing...It's a wonder that 20 year old model for a game is still so much damn fun!
The game pans out in typical Mario fashion. Get from point A to the end castle and jump the pole. You'll have to chase after Bowser (or little Bowser in this case) and make your way through various worlds with varying things to see and challange. There is a map where you pick your level, most like SMW, and there are some visible 'hidden' areas to unlock if you pry a little. Within each of the levels are giant star coins, 3 per level, and collecting them will help unlock little toadstool shops along the way, or possible alternate pathways to travel.
I've been playing Super Mario Brothers for 20 years now, and this adventure still has me yearning for more and more. It's great fun, it offers a great challange at times and also comes packed with multiplayer and minigames for added enjoyment. Until I got my hands on this game, I wasn't sure how it would turn out, but it turned out remarkably good. Even if you aren't a long time fan of the series, it is still an amazingly well done side scroller for the DS.
Whoever said that 2-D games were a thing of the past needs a swift kick to the rear. If companies can still create side scrollers this much fun, I hope I'll be playing them for another 20 years. After all, fun is what video games are all about.