The good news is Throne of Atlantis is still fun to watch. Its story is better paced than War, which was basically about meeting the League and watching them fight everything for an hour. Action sequences are well-constructed with satisfying payoffs and take place in a wide range of locations. (My personal favorite is the Atlantean attack on Arthur's lighthouse.) Throne of Atlantis also borrows some of the monster designs from the New 52 Aquaman series, including a giant Trench monster that really deserved more screen time. If nothing else, Warner Bros. animation team still puts together a slick production, even if it can never match the beloved DCAU.
One thing that irks me however is a problem across DC's new animated continuity: High levels of violence. Mera is especially prone to this, wielding her water powers to literally maim and decapitate enemies, leaving them in bloody chunks. (And considering most of these opponents are Atlantean military, presumably that led to some awkward conversations. Good thing her boyfriend becomes the king.) But even the Justice League resorts to extreme violence, dispatching Trench creatures and Atlantean soldiers in ways that are impossible to recover from. And that's not getting into collateral damage, like when Shazam hurls enemies through skyscrapers after Batman said evacuating the city was impossible. Way to go, Billy Batson.
The issue isn't the violence itself - although I'm sure many parents will cringe seeing their kids watch it. Even Man of Steel, which was criticized for wiping out Metropolis, only had Superman resort to murder in a single extreme case. But when you hear Superman say he's going to shove Ocean Master's trident down his throat and you believe him you've missed the entire point of what makes these heroes engaging. Resorting to violence clashes with the mythology of these characters, even within the darker New 52. I suspect DC's animation team is trying to appeal to "adult" demographics, which also explains why Black Manta is dropping an s-bomb for no reason. But even as someone who enjoys fictional violence and profanity, it just doesn't feel right. Not with these heroes.
That said, Throne of Atlantis is still a serviceable adaptation, and seeing the League reunite here shows promise for future films. Just don't expect it to be the Justice League you grew up with.
Bottom Line: Justice League: Throne of Atlantis is a fun spectacle, even if it's not as solid as the original comic book. The League itself is largely well-characterized, and it's a genuine pleasure to see them together again. Sadly, Aquaman's origin story is lackluster by comparison, while the Ocean Master isn't an especially appealing League villain. Regardless, the film will entertain you for its 72 minute runtime, as long as you don't mind superheroes being more violent than usual.
Recommendation: Fans of DC's animated films will enjoy this, but we're not at Justice League Unlimited or Young Justice quality just yet.