The episode introduces a new character, Rex Mason. He is revealed to be an old friend of Green Lantern's, and a bit of a rival.
Rex has a good life and a good job, and we can see that Green Lantern kind-of envies his life.
Then Rex's boss Simon Stagg finds out that he is dating his daughter, Sapphire. He is angry and purposly turns Rex into Metamorpho. (Simon was the one running the the Metamorpho experiment.)
We get to see a lot of what Metamorpho can do. He is a shape-shifter and can alter his body's molecular structure. He his a good match for the Justice League, even Superman.
I liked that we got to see a lot of character develpment with the Green Lantern. We got to learn about his past, his days before being the Green Lantern.
I was kind-of disappointed to see that so many League members could be taken out by Metamorpho.
Also about how irrational Metamorpho was when he was attacking the League.
All in all, it was a good episode, just not my favorite.