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These are different in their own ways. ISS has more diversity in game play. The thing with ISS is that you get all the entertainment in the first hours. Once you have covered most of the missions and stuff, the juice of the game is gone. I recommend this game to people want short but sweet gameplay.

Watchdogs on the other hand in my opinion took deep thought. Lots of details in everything but graphics (compared to ISS). The story is fine and it stays entertaining longer than ISS. If your into Gta you will probably like this. Lots of creative ways to use your weapons in this game.
If I had to choose between the two it would be infamous sec son. It goes beyond the real world and is truly amazing.

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Warning: may feel depression when you complete ISS
 
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