Lots of coins doesn't significantly change the Mario formula.
On the last day of E3, Nintendo finally rolled out the New Super Mario Bros. 2 demos, to the apparent indifference of everyone. I was able to casually stroll to the nearest unit and stay there long enough, unbothered, to play through the three-level demo twice.
The first level is set in the expected desert world, featuring an oasis from which the Cheep Cheeps leap, and rows of brick and ? blocks swinging left and right, which often contain power ups and coins. Yes, it's a Mario game all right.

At regular intervals, you find P switches that turn the Cheep Cheeps into gold and cause them to carry a trail of coins behind them. You can kill the Cheep Cheeps for five coins, but then their golden tail falls off the level. The challenge will be to quickly catch all of the coins and kill the enemy in one well-timed jump.
The P switches will turn the other enemies into gold as well, which can then also be killed for profit, though they don't carry coins in their wake. The switch will also have other effects such as making certain pipes spit out a fountain of coins.
The red coins are back, of course. Trigger and grab them before they vanish, and you will be rewarded with either a power-up, or if you are already fully powered up, a Golden Mushroom worth either 50 or 100 coins. Those Golden Mushrooms can be acquired in other ways, for instance they can hide inside hard to reach brick blocks.
The second level introduced the Golden Flower and lets you put it to good use immediately by giving you screens filled with brick blocks for you to turn into coins. If you are too trigger-happy, however, you might destroy a platform necessary for you to reach a Star Coin. You still have three of them per level to collect in order to fully complete it.

The final stage of the demo was in a mini castle. Just like in the previous NSMB games, they are designed vertically and constantly try to trick you into taking paths that won't allow you to get the Star Coins. The level culminated with a fight against Reznors and you could defeat them in the usual way, the only difference this time being that they were sitting on, you guessed it, coin blocks.
It's hard to shake the feeling that you are playing the old NSMB on DS with rearranged levels. The game's looks aren't improved significantly, the levels' themes are the same ones we've seen before, and the 3D effect is far too subtle to be even worth turning on. Clearly, the focus of the game is different: the level design is all about speed runs and high scores, but your usual traditional Mario game also lends itself very well to speed runs, so the extra emphasis on that aspect here doesn't make the game feel new or fresh.
New Super Mario Bros U felt newer to me. The controls felt better and the level design put more emphasis on exploration, which I prefer. And unlike NSMB2, the game looked significantly nicer than the previous entries in the series. I will get this 3DS Mario game and I look forward to competing for coins with the people I StreetPass with, but those disenchanted with the NSMB series probably won't find here the significant changes to the visuals and game design that they crave.