Thankfully, being reintroduced to War's Justice League characters is lots of fun. It's a great reflection of the premise that superhero personalities don't actually get along so well, and dislike meeting on a regular basis. Batman focuses on Gotham City cases, and considers the League a distraction. Green Lantern isn't even aware he's receiving alerts because he's more interested in flirting with women at the airbase. Superman and Wonder Woman have started dating, and prefer to spend time together when Earth isn't threatened by disaster. Cyborg is the only hero who spends time at the base, and that's because he doesn't feel like a functional human anymore. Making the heroes actually track each other down makes a great post-War reunion, and even offers solid character moments along the way. (The best examples being Clark and Diana's date, and Batman's verbal smack-down after Green Lantern botches an investigation.)
Aquaman's tale, on the other hand, is a much more standard origin story. It's your typical "chosen one" arc, where a seemingly ordinary man discovers incredible abilities, isn't sure if he's ready to embrace his destiny, but does anyway and succeeds with flying colors. It certainly doesn't help that Arthur and Mera's lines, which carry the most significance in relaying what's happening to him, tend to fall flat within the rest of the script. That's not to say he doesn't have good moments, but even those tend to be on the ridiculous side - this Aquaman eventually revels in being the hero who talks to fishes, but hasn't quite made such moments epic the way the New 52 comic series did.
Still, when you have a too-simple heroic story arc, you can always balance it by making the villains more interesting. Sadly, that never happens here. Throne of Atlantis' Ocean Master might as well be Generic Supervillain Dictator #28, a character who is evil solely for the sake of being evil. He betrays his own people on multiple occasions to whip up a frenzy for war. He sexually harrassess Mera, who clearly isn't interested in his advances. He barely even uses his father's death as justification for invading the surface, and seems more interested in attacking for fun.
In fairness, this wouldn't be a bad thing if Throne of Atlantis played up the "evil for evil's sake" angle. But the movie can't quite get away from its "realistic" New 52 roots, where the Atlantean invasion was a massive political misunderstanding. In fact, I find myself wishing that Ocean Master acted more like his comic book counterpart - A violent but genuinely patriotic leader tricked into war by an advisor. Black Manta could have fit that advisor role perfectly, but the film doesn't want you feeling sorry for Ocean Master in the slightest. So Throne of Atlantis ends up in this middle ground that's less satisfying than picking a direction and sticking to it.