I had a friend who had one and it looked amazing! Just like a real console attached to a TV, and indeed it was basically a portable Sega Master System in design. I only had a gray-scale GameBoy so the display on the Game Gear was incredible by comparison.
I do remember my joy, when finding out that instead of feeding it with batteries, I could even use the power adapter of the master system to play with the Gamegear. 😄