I actually had a weirdly opposite reaction to a lot of people on this. The graphic novel version of 'The Battle of the Labyrinth' felt...smaller to me, visually. Not in a bad way, necessarily. The book has this sprawling, claustrophobic, impossible-to-map feeling that Riordan's prose nails. You're in Percy's head, feeling the disorientation. The graphic novel has to make concrete choices, so the labyrinth becomes a series of distinct, beautifully drawn but finite chambers and corridors. You lose some of that psychological vertigo.
That said, what the adaptation gains is in character expressions and action clarity. The fight with Antaeus? Crystal clear in the graphic novel. Tyson's body language and glee over the mechanical spiders is utterly charming in a way prose can't quite capture. Annabeth's frustration and worry are etched right on her face in every panel. It makes the emotional beats hit faster, maybe a bit shallower, but very directly. I missed the internal monologue, though. Percy's sarcastic inner voice is half the fun of the books, and it's necessarily trimmed.
Ultimately, I treat them as companion pieces. The graphic novel is a fantastic refresher or a visual anchor point. If someone's struggling with the density of the book, the graphic version is a brilliant gateway. But for the full, immersive, maze-in-your-mind experience, the original novel still can't be beat. The graphic novel feels like looking at a detailed map; the book feels like being lost in the territory.