Pitfall! (Atari 2600, 1982)

As stated in my review of Adventure for the Atari 2600, programmers for Atari were not allowed to a credit for their work anywhere in the game, or on its packaging, manuals, etc.  Because of this, a group of Atari's most experienced and talented programmers became fed up, left Atari, and founded their own company in 1979 called Activision.  Each programmer in Activision was allowed to make their own games, which would be credited to them (this was back in the days when you only really needed one person to program a 4-bit video game).  The greatest of these is often considered to be David Crane's Pitfall! (1982)
There are a few distinctive qualities to an Activision game.  They are often highly experimental (by 2600 standards), and typically take full advantage of the system's graphical capabilities.  Activision never restricted themselves to a single genre, and not even the confines of a genre.  They made a few space shooters (Spider Fighter, Megamania), sports games (Ice Hockey, Boxing), and some games that defy genre altogether (HERO, Pressure Cooker).  Pitfall! is one of those rare Activision games that helped invent a genre, the platformer.
In this game, you control the adventurer, "Pitfall" Harry, on his quest to collect as much gold and treasure as he possibly can in twenty minutes (one of those short expeditions), and survive the harsh jungle environment. Among the many hazards in this game are the eponymous pitfalls, crocodile-infested ponds, snakes, fire, barrels, and scorpions.  Harry can only run and jump, and if he sees a swinging vine (one of the most fluid animations on the 2600) he can use it to bypass certain obstacles, giving out a Tarzan cry.
The game is not broken up into levels, but screens.  Harry may go to the left or right in a never-ending wilderness, and every new screen he enters is randomly generated.  On one screen, he may have to hop across the heads of crocodiles, but on another, there will be a vine for him to swing by them.  One screen may have a ladder going down to the underground, which may offer a safer shortcut past hazards, or a dead-end.  Harry jumps in only one arc, making it impossible to steer him in mid air, but each hazard is designed so that Harry's precise jumps will have plenty of room for execution.
As common as they would become, platformers were a pretty rare kind of game in the early 1980's.  Mario had gotten the ball rolling with his arcade smash Donkey Kong, but the genre still had a long way to go to the  platforming opuses on the NES and SNES.  Pitfall would get a sequel on the 2600, called Pitfall II: The Lost Cavern which made several improvements to this first game, including a bigger map to explore, but was just not the same as the original.  The later Pitfall games on the NES, SNES, and Genesis would all be catastrophic, some infamous, failures.  David Crane would eventually make the NES cult hit A Boy and His Blob.  This classic Atari game will always live as one of the best, and most influential games in the system's library.