New Super Mario Bros. is very much in the same vein as the other hand held Mario games, as it should be.
The graphics are as simple and pleasant as you might expect. Very clean and very colourful. The sound is a joy, full of fitting music and sound effects. One of the new additions is the mega mushroom, but that's minor, and level 1 aside, is only needed to get coins.
Gameplay-wise, NSMB is as fun as ever. If you want to blitz through the game, it'll be simple. Easy puzzles allow you to do that. If you try to get all the coins, that's a bit tougher. You're required to use Mario's various bonuses to beat obstacles, and even 2 of the worlds must be unlocked using them. A few unique puzzles are a joy to play through. There's a lot of variety in the boss fights, even if almost all of them follow a similar pattern. Occasionally the levels can feel a bit similar on the worlds, particularly on the ice world and water world, but they're still entertaining.
One of the few downsides is minigames (as though you'd use them anyway). Very few of them are any fun, and those that are quickly lose their fun.
Overall, New Super Mario Bros. is well worth your time. Sticking to a winning formula with a sheen, Nintendo delivers an impressive game with unique levels. Good fun.