Incidentally, along with Shazam & Aquaman, I also picked up a DC movie I've always been morbidly curious about: Superman: Brainiac Attacks. It's an animated Superman movie that uses the art style & most of the voice cast from Superman: The Animate Series, so it's kinda...sorta...a "lost" DC AU movie, but...not really.
I went into this movie expecting a total trainwreck that based on its reputation, but it's not actually that bad. In fact, I'd say it's about on par with a C-Tier Superman: TAS/Justice League episode. The animation is typical DCAU-caliber work, the voice acting is excellent, and the story is not all that far off what you'd see in a typical Superman episode of the DCAU.
Where the movie falls flat with me is how it fails to commit to a particular style. The movie may LOOK like S:TAS, but it has none of the musical theme from that series. Instead, it seems to rely on an odd variation of the John Williams Superman theme. Luthor is not only voiced by Powers Boothe instead of Clancy Brown (the best Lex Luthor), but his character seems to be modeled after the Gene Hackman Luthor. He just has a lot of goofy dialogue and bad jokes that just don't work for the character. Likewise, Brainiac is now voiced by Lance Henrickson instead of Corey Burton, and his character seems more emotional than we've ever seen the character. Meanwhile, Lois; Superman: Jimmy Olsen; Perry White; etc. all DO have their Superman:TAS voice actors and are very much in character with those versions. The two styles just don't fit together.
Overall, eh...it's alright. We DCAU fans are spoiled when it comes to great storytelling, and by comparison to the proper DCAU this film does not hold up well. However, on its own I thought it was OK.