Having rewatched the episode in late night repeats a few years after first viewing, I'd note that this is really the kind of episode which demonstrated why the series had to change after two years. It was impressive in its time, but really in hindsight it's same-old-same-old. League show up, have a pointless fight (battling the Atlantean Navy), gripe a little, have a long fight with Deadshot, part 2, another fight, a weak capture scene, they escape, another fight scene, they resolve the problem.
Now, these are good fight scenes. And Aquaman gets a welcome shot of testerone. But really this was kinda the standard template they used over and over again for two bloody years. To some degree, this is the kind of episode that "Greatest Story Ever Told" mocks - big pointless fight while some schmuck in the background plays clean-up.
This episode is padded. It's the kind of story that could have been told in 30 minutes, and it's hard to watch this and say, "Well, we should keep on doing two-part 60 minute-total episodes." The Deadshot thing is there just to show that Deadshot is cool - the audience already knows that Orm is a no-goodnik. We don't need a 10-minute fight/chase sequence to set up the revelation.
And a lot of the first two years are like this. There's a few times when the build-up is worth the extra time - "Injustice for All" and "Legends" are good examples, to build up all the characters for the former and to maintain the suspense and the feeling of loss at the end for the latter. But they're few and far between.
I think the 30-minute JLU episodes forced the writers to cut the garbage and compress things...and the characterization stands out more when you do that too.
What else? Mera has very little personality. Orm is arguably the worst villain in the entire series. At least Imperium looked creepy. Orm has almost no personality, and no real fighting skills. He needs (underwater) land mines to take out the League - ooohh.
Aquaman is really the standout here, and you have to wonder to some degree a few years later...where did it go? For a guy with all the responsibilities of rulership, he sure has a lot of time to show up in Season 4 crowd-shot cameos these days. It's not just contrast to the Superfriends non-entity, but actual decent writing that makes him a decent character and it's easy to see why him and Green Lantern butt heads - they're both basically military/command types.
Overall, this is a fairly good episode but these days with the advances in storytelling that the team has perfect for JLU, it really doesn't stand out much or make much of an impression.