For a mobile Mario game, this was a good first start. Compared to traditional 2D Mario games, the mechanics of jumping, collecting coins, defeating goombas are all there, but the main differences are that it's an automatic runner with touch controls. The controls are very simple - touch to jump, hold down for a higher/longer jump. You're also encouraged to time your jumps on enemies to string combos for more coins, and to help reach high up places. In the Tour mode, there are a few set worlds with individual levels to play through.
Completing these are usually pretty easy, but the challenge is in collecting the 5 colored coins. First you get the 5 pink coins, which unlocks the purple coins, and finally the black.
The difficulty of getting all 5 black coins in one run is pretty high in most cases, but that's what makes replaying the levels fun. There are some secret paths to find too which brings more variety to these otherwise bite-size, simple levels.

The other main mode is Rally, where you compete against the ghost of another player to collect the most coins in one run. The game offers you 5 different opponents to choose from, each in a different level. The airship is probably my favorite since you can string up big combos jumping on cannonballs. The ghost house has more of a puzzle-solving aspect to it, where you collect keys to get to the next area (and have to do so quickly to get more coins). This mode is also linked to MyNintendo - playing it once a day nets you 10 platinum coins, and 3 victories a week earns even more. That's the main reason I'm still playing this, I'm a junkie for the MyNintendo real world swag you can buy with platinum coins.

Apart from those modes there's also a hub, the mushroom kingdom, which you can build out with the stuff you collect from completing levels, rallies and events. These can include houses for characters, which then unlock those characters to play as.

I'm convincing myself that this is worth 4 stars and I'm bumping up my rating, it really is a good game even if it's not a great Mario game. Yes it may be overpriced for mobile, but it's often on sale for $5 and with no ads, it's a great experience.