PLATFORM ADVENTURE
Forerunners
The pre-Metroid era (ca 1979-mid 1986) of Platform Adventure games was a time when basic genre concepts like platformers and action adventure games themselves hadn't been fully established yet. As such, you tend to see some of what we now see as defining traits represented in each listed game, such as exploration-focused areas and permanent character upgrades, while others are missing. Or traits associated with other genres such as Rogue-likes or Point & Click Adventure games being combined with these traits and resulting in games that don't fit neatly into one category. For the most part these games are severely limited by the technology of the time as well.
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For example, the first scrolling platformer, Jump Bug (1981), is a mostly auto-scrolling game where the player avatar is always bouncing. Donkey Kong from the same year is single screen with no mid-air control or momentum-based movement. Pitfall 1-2 (1982/1984) are flip screen games with no way for the player to attack. The first proto Zelda-like​ Action Adventure games, Adventure (1980) and AD&D: Cloudy Mountain (1982), were establishing world structure, tool gating and an exploration focus, but lacked the in-game story, NPC interaction and character upgrades of the now more famous The Legend of Zelda (1986).
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Games on this and the generational pages are sorted by year, from oldest to youngest. If you're mainly interested in what to play next, I've sorted the games on each year's page roughly in order of how well I think they've held up and what they did for the genre.