The Game Gear was released in Japan in October 1989, in the US the following year and in Europe the year after that. It was indeed superior to the Game Boy both graphically and ergonomically, however, its three hour battery time (compared to the Game Boy's 10-35 hours) was a major weakness. The portable saw its first version of Sonic in 1991, which was to be the first of 10 Sonic titles on the system.
Over 240 games were released for the Game Gear. After a successful few years, it saw its end in 1997.
I remember it had an optional TV tuner as well which never worked that great but was good for a while on a trip to Wales one summer!