"Released in Japan on October 6, 1990, Sega's first handheld console featured a 160x144 pixel screen, that could display 32 colors out of a palette of 4096. The Game Gear was the second best selling handheld system of its era, selling ~11 million units.
Despite vastly superior graphics and a more ergonomic design, the Game Gear did not achieve nearly the success of Nintendo's Game Boy. Contributing factors included a price of $150, compared to Game Boy's $89, and significantly worse battery life.
The Game Gear's design was very similar to the SEGA Master System, and an adapter was sold which allowed it to play any SEGA Master System game. Another unique accessory was the TV Tuner, which turned the device into a portable television.
Source: User summary (walkie), most information from ."
Source: Wikipedia, "Sega_Game_Gear", available under the CC-BY-SA License.