If you loved Godzilla: Planet of the Monsters, try Godzilla: City on the Edge of Battle
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

Godzilla: Planet of the Monsters
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Godzilla: City on the Edge of Battle
What they share
Both films are directed by Hiroyuki Seshita, Kobun Shizuno, and they sit in Animation / Science Fiction territory. If that's the register that drew you to Godzilla: Planet of the Monsters, the second film will land in a comparable space — through a different lens.
What Godzilla: City on the Edge of Battle is
Halo without Master Chief. After twenty millennia, humankind returns to a Godzilla-dominated Earth, seeking a weapon lost to time: Mechagodzilla. This animated installment delivers kaiju action and existential pondering in equal measure.