i had atari lynx, which was years ahead of its time. not only in color, 16-bit graphics (before SNES was even out, if i remember correctly).
it was fairly large, but the design was cool. biggest drawback i noted was its weak game selection and battery EATING.
gameboy (the original, and the later 'color' version) was able to survive and thrive because it was smaller (not really pocket sized), had long battery life, and a huge game selection.