If you loved Devilman - Volume 2: Demon Bird, try Mobile Suit Gundam: The 08th MS Team - Miller's Report
A bridge between a film you've already seen and one most people haven't. Mobile Suit Gundam: The 08th MS Team - Miller's Report has roughly 3.4× fewer votes than Devilman - Volume 2: Demon Bird — it's a deeper cut, not a mainstream recommendation. Here's what they share, and what the second one does that the first one doesn't.

Devilman - Volume 2: Demon Bird

Mobile Suit Gundam: The 08th MS Team - Miller's Report
What they share
Both films are directed by Umanosuke Iida, and they sit in Action / Animation territory. If that's the register that drew you to Devilman - Volume 2: Demon Bird, the second film will land in a comparable space — through a different lens.
What Mobile Suit Gundam: The 08th MS Team - Miller's Report is
You investigate a mobile suit team in the jungles of Southeast Asia. Their recent skirmishes raise questions among Federation leaders. But the deeper you dig, the more tenuous the battle lines seem. Iida and Kanda's OVA episode offers a glimpse into the UC timeline's moral ambiguities.