From LXF Wiki
The Game Gear was Sega's attempt to break into the new handheld console market jumpstarted by Nintendo's Game Boy. A shiny black unit encompassing a colour screen, the Game Gear was technically almost identical to the Master System -- and therefore much more powerful than the Game Boy. Many Master System games were ported over; the Game Gear continued after the Master System stopped being sold, and it later saw a number of quaint Sonic platformers as a result.
Ultimately, the Game Gear lost heavily to Nintendo's handheld. The unit's battery life was very poor, requiring 6 AA batteries to power the colourful backlit screen. Typically, the batteries died after two or three hours of use -- in contrast to the 10+ hours for the Game Boy. Sega later re-entered the handheld market with the Nomad, a portable Mega Drive system with many cosmetic similarities to the Game Gear.
As with most consoles, the Game Gear was shipped with a game that few people liked and no one really wanted. In this case, it was Columns, a poor rip-off of Tetris, but somewhat similar to the Lumines game that ships with the PlayStation Portable. However, other games for the Game Gear worked quite well - anyone who ever played Sonic the Hedgehog will remember the marvellously crackly "Say-gah" start-up sound that really could have been saying anything at all.
TODO: What GG emulators are there for Linux?