Years ago, I've always been a fan of the old Superfriends cartoons, and even more so of the more action-oriented Superfriends vs the Legion of Doom episodes. But while it was cool to have a direct hero vs. villain series back in the 80s, they were always a bit too simplified and kiddy. Now, since we were all kids at the time, that's really not something we could help. Now that a lot of comic fans these days are grown, it's really nice to see that some of our cartoons have grown with us.
Which is probably the best compliment I can give to Justice League Unlimited. I've always liked the original Justice League series (which comprised only of the core DC heroes). But when they added the 'Unlimited' to the title and turned the League into an army of superheroes, I just freaked. It was awesome to see characters like the female Doctor Light, Black Canary, The Creeper, Wildcat, Fire, Red Tornado and countless others appearing, even if just in cameos. Nobody had ever had the ambition to do this- certainly nothing from competitor Marvel Comics. It was incredible to just show off your Universe like this, and JLU arguably has made it's own mark as having a setting and back story that is as gripping as the actual comics.
Justice League Unlimited's best plots of course have to do with Project Cadmus, the shadowy government organization dedicated to creating solutions to the possibility that the Justice League may go rogue. Led by the no-nonsense Amanda Waller, having unlimited resources and influence, Cadmus is a great counter-group against the seemingly all-powerful League. The latter episode Panic In the Sky, where the Watchtower itself is attacked by an army of clone superhumans, is easily the single best superhero battle I've ever seen, animated or live-action.
But along with the action and multitude of superhero cameos, what surprised me is the maturity of the series. There are things taken up in JLU (and even in companion series like the Batman titles) that years ago could never have been thought of- among them, the topic of death. In the (unaired) JLU season finale "Epilogue", this is shown in a poignant scene between Batman and the young, dying supervillain Ace (of the Royal Flush Gang). The dialogue, the mood and Batman's actions (or non-action) is touching in a way I never thought I'd see in a superhero cartoon.
In terms of animation style (Bruce Timm's art style ROCKS!), voice acting (JLU regularly uses veteran actors among its vocal performers) and stories, JLU simply is the best comic to animation title I know today. I can only hope that the next season doesn't take too long in coming. That would be true injustice.
Addendum: Justice League Unlimited's FIFTH Season (or Season 3 as JLU) will continue to focus and give light to other heroes in the DC Universe, as well as signal the arrival of JLU's version of The Legion of Doom, led by Gorilla Grodd. Wowsers! It's gonna be awesome.