This game is legendary for its extreme difficulty. On the surface, it appears to be no more than a Ninja Turtles ripoff, but once you play the game, you'll know who the real anthropomorphoid heroes of co-op brawling are. Acclaimed developer Rare definitely put all they had into it; Battletoads is perhaps the best looking NES game ever, from a graphics standpoint. Though it came out late in the lifespan of the NES, Battletoads definitely gave gamers a reason to delay switching to the Genesis or Super Nintendo.
This game truly had it all. Musclebound heroes with all manner of weapons, from lasers to flamethrowers. An intense jungle setting with an alien base crawling with bad guys intent on killing you. And best of all, it was one of the earliest two player co-op titles. One little known fact about Contra is that it was a port of an arcade game. The removal of a level selection map was balanced by the lengthening of most of the games levels. A brilliant game, Contra went on to spawn an impressive number of sequels over more than twenty years. This game is the first cooperative gameplay experience I can remember in my own gaming lifetime, and it's very much deserving of the number one slot in this list. Read more about Contra in this early Co-Op Classics article.