Kung Fu — Up the Tower, One Floor at a Time
An early NES brawler that defined the genre's template.
Kung Fu (1985, arcade name Kung-Fu Master) was one of the early NES games, and it's a foundational beat-'em-up. You're Thomas, climbing five floors of a tower to rescue Sylvia from Mr. X, punching and kicking through waves of grippers, knife-throwers, and henchmen.
It's simple (move right, hit things, fight the boss, climb), but the responsive controls and steadily ramping difficulty made it endlessly playable, and it laid groundwork the entire side-scrolling action genre would build on.
For a launch-window cartridge, it holds up shockingly well. Sometimes simple and tight beats big and complicated.