Really depends on where you're browsing. Scrolling past a million thumbnails online, a cover's gotta snap my eyes to it, you know? A striking image, a weird font, a color combo that pops – that's what makes me pause the scroll and actually read the blurb.
But if I'm already deep-diving a specific author or series, the cover matters less. I'm there for the words. Though, I'll admit a terrible cover can still make me hesitate, like it screams 'self-published in 2005' and I wonder about the editing. A good one sets a mood promise. That minimalist, moody cover for 'Piranesi' perfectly hinted at the lonely, architectural wonder inside without spoiling a thing.
In a bookstore, I'm way more tactile. The feel of a matte finish or embossed title, the weight – it all gets factored into the 'do I want this object on my shelf' calculation. A cheap-feeling cover sometimes subconsciously makes me doubt the quality inside, which is probably unfair but true.