With this very popular mod, instead of being a robot and messing around with a friend, you are Chell… twice. If you don’t want to play a story you already know and you’d rather play alone, Thinking with Time Machine is the Portal 2 mod for you.
This is even more true when taking into account the huge amount of user-made maps focused on cooperative gameplay. Either way, being one of those funny robots is always worth it. It can be all about killing your partner in the most treacherous ways, or finding the sweet momentum of teamwork. Besides having a really amazing single-player story, the co-op mode in Portal 2 is what keeps you going back.