I'd say the first Fallout was an industry changing game. At the time and still today you'd find many hundreds of thousands fantasy role playing games with spells, wizards, and classed based characters. Fallout sets itself apart from those other games by letting players be the type of person they want to be by letting them select from 3 of 18 skills and determining their stats and even option of picking 2 traits that each come with their own pros and cons. The game also introduced the idea of perks which added bonuses to the players skills and stats, the perks system was also a major influence that it has found it self in many other games to this day.
The game set's it self apart from many other role playing games by allowing the players to have a large amount of freedom and to chose how they want to play the game. For example the game offered a sense of grey morality and the choice of whether or not an action was right or wrong was up to the player rather than the game itself. Players could chose to be evil, good, or just a neutral/in between type of person. They could also chose their own play style from violent and aggressive, diplomatic and scientific, or stealthy. In addition to that, the player's choices and freedom usually came with consequences as your actions shaped the world around you and could have a impact on your character. The even offers a large open world and many non linear quests to chose from. Any quest or problem can be solved through various means ranging from peaceful to violent which allowed for players to play the game in many different ways which in turn offered large replay value. The game also very less linear from it's successors by letting the player travel to any location and skip any quest. If they wanted to, they could beat the game as soon as it started or visit locations and do quests in random orders.
