I spent a bizarrely long afternoon comparing all my editions for this. The original UK adult Bloomsbury covers by Clare Melinsky are shockingly literal sometimes. 'Prisoner of Azkaban' has the full moon, the Whomping Willow, and the stag Patronus all woven into the tree bark and shadows. It’s like a Where’s Waldo of plot points. But they feel a bit static to me, more like a symbolic poster.
For sheer, chaotic ‘everything but the kitchen sink’ energy, the original Kazu Kibuishi Scholastic paperbacks win. The 'Half-Blood Prince' cover is a masterclass in cramming: Dumbledore’s withered hand, the inferi in the lake, the locket Horcrux dangling, the green potion, and the Astronomy Tower duel all in one swirling image. It’s almost too busy, but you definitely know what you’re in for. My niece prefers those because she likes spotting things before she reads.
The minimalist trend with the house crests or the recent MinaLima designs? Gorgeous, but they trade plot clarity for aesthetic vibe. Which is fine, but not what you’re asking. For a cover that spoils the whole book in one glance, it’s the Kibuishi set, hands down. They’re like a visual spoiler alert.