Why does the Streets of Rage series have as big of a following as it does? None of the games were great. They were mediocre Double Dragon and Final Fight clones.
I never understood why the Sonic the Hedgehog series became popular, either. The original Sonic the Hedgehog game was decent, but nowhere near as deep, polished, or innovative as Super Mario Bros. 3, Super Mario World, Mega Man II, Donkey Kong Country 2: Diddy's Kong Quest, etc.