This episode finally deals with the Martian Manhunter who has been relegated as coordinator of the JLU from the satellite. People have surmised that the writers have been keeping Martian Manhunter on the sidelines because his powers are too varied and versatile to write an effective suspenseful villian showdown. This may or may not be true, but the writers handle this situation head-on, by incorporating his isolation as a character flaw.
Wonder Woman's character is really bolstered here, first by confronting Martian Manhunter, and second by reluctantly assuming the role of novice diplomat, when the Wonder Woman of this series is more confrontational, aggressive, and generally more Amazonian in nature than her idealized incarnation in the comic books. I liked the throwback to the Linda Prince Wonder Woman with the twirling, it helps solidify the fact that the writers are attempting to explore her character both in and out of costume.
The cell-shaded sketches of Prince John as Grodd told his stories, were visually compelling and amazing. It worked perfectly with the story. They should use that style again in future episodes.
Overall though, the haunting ending is what makes this episode special. The way Martian Manhunter realized the things he need to change, from Prince John's tragedy was moving. The cutting between his traditional Viking funeral and J'onn saying goodbye and merging with humanity, all over Coleridge's redemptive stanzas in the Rime of the Ancient Mariner was one of the most powerful and affecting dramatic endings that I've seen for any animated series.