The 'Overlord' anime has three movies so far, but they aren't entirely new content—two of them are compilation films that recap the first season. The first, 'Overlord: The Undead King,' covers the initial arc, and the second, 'Overlord: The Dark Warrior,' continues from there. The third movie, 'Overlord: The Sacred Kingdom,' is the one that actually expands the story, adapting the 'Holy Kingdom' arc from the light novels. I remember being hyped when it was announced because fans had been waiting for new animated material after Season 3 ended. The compilation films are decent if you want a refresher, but 'The Sacred Kingdom' is where the real excitement is—seeing Ainz and the gang in fresh adventures just hits different.
If you're diving into the franchise, I'd recommend watching the main series first before jumping into the movies. The compilations might feel redundant if you’ve recently binged the show, but they’re great for revisiting key moments. And 'The Sacred Kingdom'? Pure fan service in the best way—more world-building, more Nazarick shenanigans, and that classic Overlord mix of strategy and dark humor.