The song without autotune sounds detached.

BTW, perfect speech synthesis should be achieved before speech recognition and certainly long before true AI, like GlaDOS. So the developers' decision to indicate GldDOS's machine-nity by distorting her voice with autotune seems contrived, stereotypical and "unscientific". Kubrick probably knew this when he gave HAL9000 a normal human voice back in '68.