It looks like an extension of the Superman Animated series, but it really isn’t. Brainiac Attacks is missing all the brains that was such a highlight of the Superman Animated series and in extension most of the rest of the Animated DC Universe. Sure, the creators of this movie always said it never was part of that special continuity nor did it even try, but when you use one widely known style for your movie, you invite, no, you force people to compare. And it doesn’t look good.
The one reason why Luthor was always one of the best villains of Superman is that among all those aliens and gods that populate the show he was merely human, but one who could easily best them all. A bit like a negative of Batman, who was merely human among all the high-powered superheroes and who still managed to be better than most of them. For no apparent reason Luthor turns into a complete buffoon in Brainiac Attacks.
Not that the others characters fare much better, but at least their characterization is only slightly bad, but Luthor’s is completely fucked. The only one who doesn’t feel like he’s taken some drugs is Brainiac and even he does some fairly nonsensical stuff, like attacking the city later on for no reason. Overall, this movie has to be seen for just one reason: to realize that not all the Warner Brothers animated stuff is automatically gold.