It really is very terrible. It recalls Justice League season 1 or Superman: Doomsday (the first "Death of Superman" animation) in that it looks like Timm handed some scattered story notes to a useless fanfic-tier hack writer to grind into garbage. Every single line of dialog is awful, the established characterizations are subtly off, the jokes are unfunny, it's heavy on exposition yet still leaves significant events wholly unexplained, and there's no sense of pacing and nothing that happens seems to matter. It's also childishly edgy, with a bunch of excessive blood and profanity. A character exlaims "fart nuggets" at one point, so a millennial must have written this. Superman actually cries out "Great Rao!" in surprise, which is as dumb and jarring as giving Adam West lines to Kevin Conroy. The Big Three barely interact with each other and have zero interpersonal chemistry. A few plot points are direct repeats from episodes of JL/JLU.
The animation is stiff and choppy but the choreography and staging of the fight scenes is actually better than what we usually got on JL/JLU… Batman gets to do cool martial arts, Superman (usually) remembers he has super-speed and gets to do Znyder/DBZ stuff, although because Bruce Timm, he's still not much better in a fight than Batman and gets the crap kicked out of him constantly.
If you've seen any piece of media in the past 10 years, and I envy you if you haven't, you should be able to guess Jessica Cruz's character arc:
>doesn't believe in herself
>screws everything up because she's an idiot
>learns to believe in herself
>becomes more powerful than everyone else and best at everything and everyone loves her
>people she got killed are still dead
For a DCAU fanboy (me), the closest thing to a redeeming point was the continuity and DCAU fanservice and finding out what happens after the JLU finale, and they really try to establish that yes, this is supposed to really be the DCAU, not just recycled designs:
>we see statues of the DCAU original 7
>Martian Manhunter and the GL Corps are stated to be away fighting a war on the planet Rann (same one from YJ, and probably some comics idgaf about), who knows what about or why though
>Joker is stated to be in Arkham and Tim Drake is brought up, so we're clearly pre-RotJ flashback
>Because Bruce Timm: Harley and Ivy have rather lengthy but unvoiced cameos, some other Arkham inmates appear
>Hawkgirl is acknowledged and stated to have returned to Thanagar, although the why and the current state of Thanagar are left to the imagination
>John Stewart isn't really mentioned, but is presumably alive (maybe off on Rann), considering he apparently lived long enough to get to know his son, so who knows where Cruz's ring came from. Flash gets nothing that I noticed.
>We see a GL space travel at warp speed – it bugged me that JL always depicted them slowly floating through space
>A GL ring is destroyed and reassembled, possibly explaining how John Stewart fixed his ring
>Although DCAU Superman does need to breath, he has been shown to hold his breath and briefly fly into space before. However, in this thing, he flies to the sun in a couple of minutes at FTL speed, which seems way too fast for this Superman, especially since he couldn't do the same in a JL episode in a nearly-identical situation ('Eclipsed'). And he doesn't seem worried about air in the least.
>Supergirl being totally unacknowledged is distracting
>Miss Martian has powers J'onn never did, like making other people intangible along with herself
>Superman and WW wear their safety belts in the javelin, lmao. This happened in JL season 1 iirc, probably because standards & practices demanded it. This could almost be a coded message from Bruce Timm that he knows this movie sucks
So you see there's quite a bit of shoehorning and handwaving to get around the fact that the story doesn't fit into the DCAU very well at all, plus what may be actual mistakes, and one wonders why they even bothered, or, if they simply had to bring back JLU for money, why this particular story was used to do it. Maybe the DCAU connection was added as a calculated marketing move to prop up a feature they knew nobody would have cared about otherwise? I know I wouldn't have bothered with Limelight: The Beginning: A DC Animated Original, which is what this actually is, so they tricked me at least. DC still can't even bother to hype it up as the alleged return of their actually-good animated universe, it's just another DVD cashgrab-of-the-month.
In conclusion, the DCAU is back! but with typical DC Animated Feature quality, i.e. kindergarten-level writing with PG-13 content. If anything it's even worse than average for them.