If you loved Legion of Super-Heroes, try Justice League: Crisis on Infinite Earths Part Two
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.
You already loved

Legion of Super-Heroes
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Justice League: Crisis on Infinite Earths Part Two
What they share
Both films are directed by Jeff Wamester, and they sit in Action / Animation / Science Fiction territory. If that's the register that drew you to Legion of Super-Heroes, the second film will land in a comparable space — through a different lens.
What Justice League: Crisis on Infinite Earths Part Two is
You fight alongside superheroes against an endless army of shadow demons. But even combined power may not be enough. The Monitor's secrets threaten the last defense.