 The cooperative puzzle solving aspect was highlighted as a valuable addition to the game . Welsh called the cooperative mode " one of the most satisfying and genuinely collaborative gaming experiences you can have with a friend " . Onyett wrote , " Valve knows how a good co @-@ operative mode requires a game design that doesn 't simply encourage but requires you to work together . In Portal 2 , communication is vital to success " . Several reviewers praised the non @-@ verbal cues that players could initiate to work with their partners . Portal 2 was praised for the amount of detail in its design , sound , and music . Nelson credited the " sheer amount of detail " put into the game 's world , and wrote , " it all feels very real and natural with brief moments where you 're simply sucked into this world " . Onyett was impressed with the amount of visual details and capabilities Valve achieved from their Source game engine and that the added details and animations of the levels " consistently serv [ ed ] not only to entertain the eye but to expand our understanding of the game 's characters " . Hoggins wrote that the game 's world reacted to the player @-@ character Chell 's presence " in a startlingly organic way " , and praised Valve 's design as " an achievement of world @-@ building that compares favourably with BioShock 's underwater city of Rapture " . 
