Sonic the Hedgehog 2's gameplay is largely the same as its 1991 predecessor. A side-scrolling platformer, the player controls Sonic the Hedgehog as he runs at high speeds, defeats enemies, and overcomes obstacles. The story takes place following the events of the last game; Sonic returns home to find that Dr. Robotnik has taken Miles "Tails" Prower, so he heads off to find him before it's too late.

Like the original, Sonic collects power-ups (such as boosts of speed and invincibility) that give him temporary powers, and rings to protect himself from being hit by enemies or obstacles. Sonic starts with three lives; if he is hit without carrying any rings, falls into a bottomless pit, drowns, or goes past the act's 10-minute mark, he loses a life. Losing all lives results in a game over. There are some changes, however; checkpoint and shield item boxes are absent, and Sonic can now collect rings he drops when damaged. Certain elements present in the Sega Genesis version of Sonic the Hedgehog are also implemented, such as the ability to smash through walls and run through vertical loops. The game also features modes of transportation for Sonic in which to maneuver the levels, including minecarts and hang gliders.

The game is split into seven levels called zones, each comprising two main acts and a boss fight with one of Doctor Robotnik's robots. While the 8-bit Sonic the Hedgehog stages borrowed thematically from those in the original 16-bit Sonic game, Sonic 2 features original levels to differentiate itself from its 16-bit counterpart. At the end of each main act, the player hits a signpost, which will spin and land on an image; it can award bonuses depending on the image it settles on. There are six Chaos Emeralds to collect throughout the stages. If the player collects them all, they will be able to save Tails at the end of the game.