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Off course not, those other games are themselves and the only thing is relationship between freeman and them.

While you don't have to play those other games to understand what is going on, I recommend you do as you never know what future references valve will use in their games. All games except Opposing Force are canon and there is still speculation that even Adrian Shephard might be used later on by valve. It all comes down to how much of a diehard fan you are.

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