This game is wonderful (please laugh).
This game is a breath of fresh air for 2D Mario. Now I'm not as hard on NSMB as most people are (I think they are solid and well made 2D platformers), but this game is on a whole other level. Everything just feels so fresh, both the new stuff and returning elements. And no aspect of the game overstays it's welcome, but unlike some games it doesn't go too far in the opposite direction. If a mechanic is fun enough it will turn up again in a later level.
And then there is the topic of the Wonder Seeds. Before we even get into the main gimmick just having some of the collectaphon elements of 3D Mario is a great way to spice up the more linear 2D offerings of the series. And as for the wonder effects themselves, they are a brilliant way to add variety to the gameplay. A lot of them end up altering the game in ways that go beyond what a mere stage gimmick or power up can offer.
And on the topic of power ups each one is a joy to use. The fire flower obviously returns and is the typical offensive move it has always been. But all of the new ones go a long way to making the game stay entertaining. Surprisingly the game is lacking the now traditional flying power up, a welcome change in my opinion as I believe they can sometimes be a bit too OP.
But power ups aren't the only way to change up your moveset. New to Wonder are the badges. These alter how the player controls in various different ways. From extra moves like a glide, more passive abilities like the higher and floaty jump usually reserved for Luigi (all characters except for Nabbit and the Yoshis have the same moves and physics), helpful perks that make the game easier like getting a free super mushroom when staring a level/respawning or challenge badges, such as constantly running without being able to stop.
All that is to say don't pass on this game if you think 2D Mario has been getting stale.