Complex sentence: Johns felt like there was an interesting story to be told in Rebirth with the dichotomy between Superman--an alien who embodies and is compassionate for humanity--and Doctor Manhattan--a human who has detached himself from humanity.
Split into simpler sentences: Johns felt like there was an interesting story to be told in DC Rebirth with Doctor Manhattan. He thought there was an interesting dichotomy between Superman--an alien who embodies and is compassionate for humanity--and Doctor Manhattan--a human who has detached himself from humanity.