I'm sure I played this game before...
There are some 'new' power-ups. There's the racoon suit, oh wait that's not new, it's from super Mario bros 3. This lets you fly and glide. Then there's the gold flower, which is new, except it isn't- it's basically a fire flower than can also turn blocks into coins upon contact with the fire. And as usual, the good ol' fire flower returns. Not Nintendo at its most creative, but the design of the levels is great, and that's what keeps you wanting more, even though it is too easy. The 3D is terrible, because it blurs backgrounds more the further you push the depth slider. Also, nsmb2 never does anything with 3D. It could learn a lot from Mutant Mudds. You can play through the whole game with two players, but player 2 will need another copy of the game.
Then there's the coin gimmick. Basically all the levels in New Super Mario Bros 2 are bursting with coins and different ways to get them. This is where Nintendo get creative, placing all sorts of new ways to collect coins, and that's where that rare gold flower comes in useful too. Just like any other Mario game, Bowser kidnaps Peach, and saving her is the goal. As usual, on top of that is star coins- three in each level, you know the story by now, and also secret exits. But now there's also the goal of collecting 1 million coins. This takes a long time, but levels are overloaded with coins, and the more skill you have, the faster you'll reach the goal of 1 million coins. What's the prize, I hear you ask. I can tell you: a new main menu screen. That's it. Coin redemption can be found in coin rush mode, though, when you play three randomly selected courses in a row and try to collect as many coins as you can, and reach the goal in a 100-second time limit. One death and it's game over. You can trade high scores via streetpass, but there are no online leaderboards, which is disappointing. However, coin rush is a simple, addictive experience and I'm surprised nobody's thought of it before.
In conclusion, this is the first Mario platformer ever that isn't essential. I'd recommend it, but it stays too true to Mario's roots.