This episode moves right into things - couple spots alien structure, one of them gets eaten/consumed (presumably), the Justice League show up, and hordes of robot creatures emerge and plan to swarm the Earth. That's the first three minutes. Then call in a specialist hero to save the day, throw in lots of battle shots, and wrap it up with a vague hint of government conspiracy.
This episode seemed a waste of Warren Ellis' considerable talents. For a guy who has written Global Authority and was selling it to the WB (unsuccessfully), this vaguely Stargate-ish tale of replicating mechanical invaders seemed imminently disposable. Hopefully they didn't pay him more then scale as a "name" writer, because all he did was what the staff writers have demonstrated they can handle.
Presumably Ellis is a fan of the Atom and/or the concept of a "scientific superhero." The Atom gets a good amount of screen time and saves the day, and gets a bit more personality as the curious-to-distraction professor type. It seems a little dumb for him to start talking instead of acting sometime, but most heroes and all villains seem to do this in the comics anyway - at least the Atom has a reason here.
Of the "main team," the emphasis is once more on the trinity of Superman, Wonder Woman, and Batman. The Flash is absent once more and Green Lantern is reduced to non-dialogue status. J'onn hangs out in the tower - it's still not clear why. You'd think being able to telepathically link the team would be useful and he needs the distance and isolation to do so, but he never does this (even though he does regularly in the comics).
We get to see maybe 90% of the League newbies here and a few of them (Vigilante, Dr. Light, Atom-Smasher) get a few cool moments. Oh, that's the cowboy on the motorcycle, the Asian woman in black-and-white, and the giant-sized guy, for those just reading this review after having stumbled across this episode and have no idea who these relatively obscure heroes are.
Generally it's another extended "spot the hero" cameo episode, though, like "Initiation"> and "Greatest Story..."
And wow, this episode had a lot of black-and-white. Dr. Light in her black-and-white episode had the perfect camouflage...
And finally we get another glimpse of the government conspiracy. Considering some of the Leaguers are weapons of mass destruction, the government's concern over an artificial one seems a little strained. Also, why did the League keep it secret and/or not check it in with the various governments? They seem to have worldwide UN-like operating status - why would they keep this secret? But presumably this'll tie in with the whole government-conspiracy story arc.
Overall, there were some neat moments of characterization and a very little bit of overall advancement, but mostly this one was entertaining but forgettable.