The game includes 50 levels in Adventure mode, which start out easy but get to be quite hard by the end. Infinite mode includes an unlimited number of randomly-generated levels, and the Kongregate version of the game has an enormous selection of user-created levels.
The game includes three speed settings: Normal, Fast, and Intense. Fast is 1.5 times faster than Normal, and Intense is twice as fast as Normal. Intense speed isn't unlocked until you finish either Adventure or Infinite mode on Normal or Fast.
Intense speed acts like a separate game mode. When you select it, your progress disappears, and you have to replay the game from Level 1. Likewise for Infinite mode, which restarts from 20% difficulty. Your old progress is restored when you select Normal or Fast.
When the game was released, the Runner was the only character. On July 2, 2012, seven new character costumes were added. Some of the costumes later became characters in Run 3, including the Student, Lizard, Gentleman, Angel, and Skater. However, at this point, the different characters were simply costumes, and had no special abilities besides the Skater costume. Like in Run 3, the Skater skates faster and jumps farther than the other characters. Other than the Skater, the costumes don't affect gameplay. A few characters are unlocked at the start, and you unlock the rest in Adventure mode, on levels 5, 10, 20, 30, and 50.