Esoteric Happy Ending: The story tries to tell us that a new generation of heroes is about, the problems with this are that there were likely millions of innocents killed due to people losing their powers, few superheroes getting over their problems, the magical characters (close friends of the heroes and entire civilizations) are still mysteriously missing, and Kyle Rayner, ultimately, ends up killed due to psychotic obsession. This isn't getting into the fact that many tech-based supervillains keep their powers and abilities, one new, superpowered being doesn't make the world better.
Narm: The Phoenix Group's new gimmicks and costumes are very lame. Martian Manhunter becomes "Green Man" who for some reason utilizes a skull motif for his grenades; Aquaman becomes "The Hand" utilizing a gauntlet with interchangeable hands; Supergirl becomes "Justice" wielding a dual mace named "The Scales of Justice" and wears a blindfold in her costume that still lets her see, apparently just so she can pull off the "justice is blind" joke. Wally West as "Red Devil" works well enough, at least (barring the fact that he considers "fearless abandon" a noteworthy attribute). The Reveal of these new identities are supposed to represent they've completed their training and have been reborn as a new generation of heroes, but you'll more likely groan at how bad their new gimmicks are.
Strangled by the Red String: Superman and Wonder Woman, considering that Lois is pretty heavily derailed in order to break up with Clark. That said, both Wonder Woman and Superman undergo some fairly odd changes in behavior and worldview to come together in the way they did.
Tearjerker: There is a genuinely affecting scene where Billy Batson yells out "Shazam" to try evoking his powers, only for nothing to work and he bitterly walks off.
They Wasted a Perfectly Good Plot: The idea of an Elseworlds story involving heroes losing their powers is an interesting idea, but the possibilities were not explored that well in this story due to a very confused Aesop, as well as heroes acting like brats. Another idea that would have worked fine is working together to find out what caused the Black Light and caused them to lose their powers.
A similar story had aliens separating the Justice League into their superpowered selves and powerless human selves. The powerless human selves reacting to suddenly not having superpowers was written far more realistically and allowed for some exploration of personalities: a powerless Plastic Man returns to crime and loses his sense of humor because being Plastic Man made him a good person, Kyle Rayner goes crazy as an artist because he doesn't have a ring to visualize all the ideas in his head, a powerless J'onn J'onnz is fascinated at no longer being afraid of fire but loses his strong empathy and becomes selfish.
Interestingly, Marvel would do something similar with one of their "What If?" issues. However, they had a way to do it that made at least some sense in-universe. It was a "What If" story based around the House of M crossover event where it ended with Scarlet Witch decreeing "No more powers!" instead of "No more mutants!", depowering all the heroes in the process. There was no moping or angsting on the part of the good guys. When Red Skull came with a powerful new weapon, new Avengers risked their lives with Iron Man suits and led by Peter Parker, who broke said weapon (the Cosmic Cube).
Also, a great many superheroes have gone through a period of being Brought Down to Normal in their mainstream continuities. For example, Wonder Woman lost her powers for an extended period in the mainstream comics during The '60s. She continued doing heroic missions all the same, albeit as a Black Widow-type Badass Normal.
Unintentionally Unsympathetic: We're supposed to feel bad for the depowered heroes for losing their abilities and finding their lives completely pulled out from under them, but it's really hard to given how much they whine and complain. Most of them don't show much interest in figuring out the cause of their loss of power or getting them back, and just sit around moping about how much not having powers sucks. The Phoenix Group does try and rebuild their lives and become heroes again, but their desire to do so is framed as them missing the feeling of being powerful and wanting to recapture it, not that they want to go back to saving lives and stopping villains.
Wangst: Superman, Green Lantern, and many other depowered heroes suffer from this. Instead of trying to make new lives for themselves or try to figure out the cause behind their depowering and a way to reverse it, they basically turn into a bunch of sad-sacks who don't even try to do anything.