Sonic The Hedgehog 4, as the title indicates, is a direct sequel to the classical series of Sonic platformers on the Sega Mega Drive / Genesis. The story continues after the events of Sonic 3 and Sonic & Knuckles, where Sonic and his friends spoiled the plans of Sonic's nemesis, Dr. Eggman (a.k.a. Dr. Robotnik), once again by destroying his Death Egg and returning the stolen Master Emerald. The victory, however, is short-lived, as Eggman is up to revenge and rebuilds and improves his greatest creations for the sole purpose of destroying Sonic once and for all.
The game does not only return to the original series in terms of story and title, but also in terms of gameplay. Sonic 4 is a classical 2D sidescroller like its predecessors and also features the same game mechanics as the old games. There are some new additions, for example the "Homing Attack" which locks on Sonic's jump on enemies, jumping pads or breakable items. One major difference are the graphics, as Sonic 4 uses polygons for the Sonic characters and prerendered graphics for everything else, so does not recreate the looks of its predecessors, unlike, for example, Mega Man 9.