While it's not exactly new territory for a sci-fi series to do the whole parasite-dream skit, it's taken to surprising depth in this instance, especially, all things considered, for a supposed "kids show".
The plot is simple enough: Batman and Wonderwoman find Clark in the fortress with a plant stuck to him. Someone is behind it. Wonderwoman seeks out whoever is responsible, while Batman tries to figure out how to get the parasite from Clark's body without killing him.
The interesting twist being that the plant grants Clark, or, erm, Kal-el to enjoy what he's always wanted - eternal bliss.
Seeing Clark living the Krptonian dream isn't really a shocker, but the level of detail and the plethora of nods to Superman mythology make it an incredibly enjoyable character piece and a jolly good romp. Again, those who made the leap from JL to JLU will surely find enough plot and character to calm those uneasy feelings about the new format prohibiting any time for real drama. This is top stuff!
And when Batman becomes infected? It raises what was otherwise a solid 9er to a 10. It was extremely cruel to have Bruce live out those moments yet again but this time seeing his father prevail, only to have him taken from him yet again. Powerful stuff.
Overall, one of the best episodes from Justice League Unlimited.