A back-to-the-basics Mario platformer that's every bit as fun as the NES original
The primary complaint I've seen leveled at this game is that it's too easy. All that really means is that most people will be able to get to the end with a little perseverance. Extra lives are fairly easy to come by - in fact, there is a trick in the very first level that allows you to easily rack up infinite lives, though it's not something you're likely to discover accidentally - however, this is offset by some particularly fiendish levels later in the game that seem designed with the expectation that you'll have dozens of lives to burn in the process of completing them. There's also the added convenience of being able to save after every castle or by spending 5 star coins to unlock an alternate path, although beating the final castle unlocks the luxury of being able to save at any time from the world map allowing you to find all the secrets at your leisure.
And there are a lot of secrets. Finding every last star coin (there are three per level) is a challenge in itself since many of the star coins are in secret areas or are in an area that can only be accessed under certain circumstances, such as shrinking Mario down to pint size so he can fit into a tiny pipe. In fact, simply completing the game in the most straightforward way possible will have you missing out on about a dozen levels and two whole worlds (yes, two whole worlds!). In other words, even after beating the final castle, there will be plenty of incentive to keep coming back for more.
If you want a break from the platforming action, there are about a dozen touchscreen powered mini-games to pass the time. Some of them first appeared in Super Mario 64 DS, but others are new. They're not especially complex, but they're a lot of fun, and there's a lot of variety. For instance, one has red and black Bo-ombs randomly entering the screen, and you have to quickly sort them into the matching colored holding area. One mistake and you explode the lot, ending your game. In another you have to draw trampolines for Mario to bounce on in an attempt to send him into various targets. The angle you draw the trampoline changes his trajectory, and if he falls you lose a life. My personal favorite is a simple five-card draw picture poker game with Luigi as the dealer. It makes me wish for a full Mario themed casino game.
The only thing I can think of to criticize about New Super Mario Bros. is that Nintendo didn't think to include an emulation of the original Super Mario Bros. as an unlockable bonus. They did it with the original Metroid in Metroid: Zero Mission, so why not here?