Double Dragon was THE huge arcade game back in the late 80's. I remember all of my buddies were waiting on the NES version, and then it was only one player. Just terrible. By the time Double Dragon 2 came out for NES with two-player co-op, we were all so jaded...it just wasn't the same.
There was a time when beat'em-ups were the biggest game genre out there, I'd say probably prior to the Street Fighter era. Once Street Fighter II came out beat'em-ups really vanished. But there was Double Dragon, Bad Dudes vs. Dragon Ninja, Combatribes, Streets of Rage on Genesis...every system had to have one.