Sonic Dash is an endless runner game. There are three lanes, and you flick a direction to switch with the aim of collecting rings and maybe avoiding enemies/obstacles. You can flick up to make Sonic leap which can jump over grounded obstacles and enemies. You can swipe down to roll under high obstacles and to defeat enemies.
When you collect a certain amount of rings, you can activate your special dash move which defeats enemies, crushes obstacles and collects rings; bascially allowing you to cover a large distance without challenge.
If you get hit by an enemy, you drop your rings if you have any, and you die if you hit an obstacle. When you are defeated, you can spend some in-game currency to revive Sonic, or accept defeat. Your total distance is then added to your total. At certain milestones, you unlock extra rewards.
With your collected rings, you can unlock upgrades which can extend your dash move or upgrade power-ups.
After completing a section, you can choose which area to go next which have different themes but the gameplay remains the same. Sometimes you will be given a boss battle. I only saw two types; Robotnik and Jazz (from Sonic Lost World) but they played exactly the same. You just dodge their attacks then eventually you just tap when the two cross-hairs meet to spin-dash them.
The graphics are very good, and the theme suits the type of game. It features simple gameplay, but well suited to mobile devices and the pick-up-and-play mentality.