Sonic the Hedgehog: 16 bit

This game is the one that everyone remembers. Compatible with the SEGA Mega Drive/Genesis it soon became one of the most popular games throughout history. It was the first installment in Sega's flagship Sonic the Hedgehog video game series and the first title to be developed by the Sonic Team.

Storyline
Sonic the Hedgehog is a blue hedgehog who lives on South Island with his animal friends. He encounters an evil scientist named Doctor Ivo Robotnik, known as Dr. Eggman in the Japanese version, for the first time. Dr. Robotnik/Eggman seeks to obtain the powerful Chaos Emeralds so that he can take over the world, and sets about transforming animals into robots to serve his ends. Realizing Dr. Robotnik/Eggman's evil ambitions, Sonic pursues him though several of the world's "Zones" before eventually defeating him in Scrap Brain Zone. Following this victory, Sonic returns home to South Island to rejoin his friends and to resume his normal life. If the player was able to collect all the Chaos Emeralds, their power produces new plant life in the Green Hill Zone, which surprises Sonic.

Gameplay
A typical in-game screenshot of Sonic the Hedgehog, taken from its first level, Green Hill Zone.
In the game, Sonic must prevent Doctor Robotnik from collecting the six Chaos Emeralds in an attempt to rule South Island. The player controls Sonic as he traverses six zones, each of which is split into three "Acts". At the end of the third act of each zone, the player faces Dr. Robotnik in one of his vehicles.

The gameplay centers around Sonic's ability to run at high speeds with levels that include springs, slopes, high falls and loop-de-loops. Hazards the player experiences include a wide variety of badniks, animals trapped inside mechanical bodies. The player must also avoid rows of sharp spikes, bottomless pits, and other obstacles.

Scattered around each level map are gold rings, a signature item of the Sonic series. Collecting 100 rings rewards the player with an extra life. Rings act as a layer of protection against hazards as long as Sonic is holding at least one ring. Shields and temporary invincibility can also be collected in order to provide additional layers of protection; however, they do not prevent the player from losing a life if Sonic be crushed by a trap, be drowned, fall into a pit, or spend over ten minutes in an Act.

Progression through the game is aided by lamp posts that act as checkpoints. In the Japanese version, if a checkpoint be activated and a life be lost as a result of running out of time, the time at the checkpoint will reset to 0:00. If Sonic lose all his lives, the game is over unless he obtained continues from Special Stages, in which case Sonic returns to the beginning of the Act with three lives.

Levels
Green Hill Zone; Tropical Island; 3 acts
Marble Zone; Lava-filled ruins; 3 acts
Spring Yard Zone; Urban city & casino; 3 acts
Labyrinth Zone; Ancient ruins & underwater; 3 acts
Star Light Zone; Urban city & night; 3 acts
Scrap Brain Zone; Trap-filled industrial factory; 3 acts
Final Zone; Robotnik's hideout in Scrap Brain Zone; 1 act

Legacy
Sonic the Hedgehog greatly increased the popularity of the Genesis in North America. After it was released, it eventually replaced Altered Beast as the game bundled with the console. In large part due to the popularity of this game, the Genesis outsold the Super Nintendo nearly 2 to 1 during the 1991 holiday season. This success led to Sega overtaking Nintendo in January 1992 with control of 65% of the 16-bit console market, making it the first time Nintendo was not the console leader since December 1985. The game featured many novel elements which contributed to its popularity and helped to promote the uptake of 16-bit consoles. The game is widely considered to be one of the greatest games of all time, placing #63 on IGN's 2007 list.

Sonic the Hedgehog added the element of speed to the standard platform formula and introduced other unique elements as well, such as the loops, springboards, high-speed devices, and the rings now permanently associated with the series. While the speed greatly contributed to the mix, the excellent execution of the platforming element was what made the 2D games shine.

The game spawned numerous sequels. While the first games in the series were platform games, the series has expanded into other genres such as action-adventure, fighting, racing, role-playing, and sports. The series has also expanded into other media, including anime, cartoons, comic books, manga, and toys.

For an idea as to what Sonic looked like all those years ago in his full pixelated glory I managed to find an image online. I think it was created recently by an artist, nevertheless this does not detract from the great visual quality and definitely gives you a feel for that retro vibe.