New Super Mario Bros. is a worthy addition to the series that doesn't disappoint.
Bad: Music isn't nearly as good; water levels aren't as fun; not particularly long; annoying save system; not as challenging for veterans.
New Super Mario Bros. is a terrific game that is a necessary addition to any DS's owner's library, not just because it's a Mario game, but because it's also very good.
It works a lot like previous games, intentionally. One button does the jump. The other one does the fireflower/dash. It still works perfectly, but this time, Mario has some new moves added to his repertoire, borrowed from the 3D entries - the butt-stomp and the wall-jump, which both control great and integrate very well into the level design. Mario also has his usual power-ups, such as the mushroom and the fireflower, as well as a blue shell power-up that renders you invincible when you crouch, and the star, which makes you invincible for a short amount of time.
The two big new power ups, though, are the mini and mega mushrooms. The mega mushroom makes you, well, huge for a limited time, and as you walk you smash everything in your way, including blocks, pipes, and enemies. The more you smash, the more 1ups you get at the end of your stint as a mega mushroom. The mini mushroom makes you mini until you get a regular mushroom to make you big again. Obviously, the mini mushroom doesn't make you any better against enemies, but it's very useful at discovering various secret areas.
Another mechanic in New SMB is collecting big coins. There are three in each level. They don't really do anything, to my knowledge, except that you can use five of them to unlock new paths to a mushroom house or a mega mushroom house, or even some levels, and an impetus for people to go play through levels just to get all three coins. Also, each time you use five of them, you can save.
The save system is a small annoying part of New SMB. Save points are very rare, and only come after a tower or a castle, of which there are typically one of each on each world, or when you spend five coins. If you don't have the coins on hand and lose your last life in a tough castle, you'll have to go back to your last save point, which means you can potentially lose a lot of progress. If not for a loophole in level 1-1, which is the only level where you can always get a mega mushroom and therefore 1ups, I would have had a significantly harder time beating New SMB.
New SMB won't take very long for experts to beat, and not especially long for regular gamers to beat either, but it does have some unlockable content. There are eight worlds, as usual, but get this - pretty much everybody who beats the game will do so while skipping two worlds. Two ENTIRE worlds, not levels, though you'll probably skip a couple of these too, and more if you find secret exits in levels which get you to a warp pipe or a cannon. Most people will want to unlock these levels and worlds, so it's a good amount of content that is lying there for you to get (plus you can see all the levels and/or worlds that you haven't unlocked, which only serves to make them that much harder to ignore).
A little extra value is added in the two other modes New SMB has, though most of it comes from one. One of them is a minigames mode that can be played singleplayer or with local wifi multiplayer, which is fun enough but will get boring after a while. The other mode is more fun, though, and is local wifi multiplayer only and can be played with two players only. No, unfortunately it's not co-op, but it's called Mario Vs. Luigi, when you and a friend face off as these characters in a battle to collect however many coins you specify. It's pretty fun, albeit a little frustrating, as sometimes whoever wins can be more or less arbitrary.
New SMB looks very good, as it should since it's 2D. Mario (and Luigi) animate sharply and convincingly, and the enemies look great (albeit mostly familiar) as well. There is never any sign of slowdown, especially in the single-player game.
The same can't be said for the sound. The sounds are terrific, as in the sound effects. The music, though, is not up to par, especially considering the standard the terrific Mario games previous to this one set. The familiar old Mario Theme plays in one spot (not in any levels), sure, but mostly, the music's new, and it's a disappointment. It's not bad, or anything, but it's disappointing considering the pedigree of the games. Not to mention the composer seems to be really into a female chorus saying 'DA' at various intervals in the music, which is annoying.
All in all, though, New SMB, despite it's faults, is well worth the purchase for any DS owner, any Mario fan, and is a good impetus to adopt the DS handheld if you haven't previously.