Rachel's voice itself might be slightly polished. Her inner monologue in the original is raw, sometimes disjointed, brimming with panic and sarcasm. In the revised version, that voice is still distinctly Rachel, but perhaps a tad more coherent and literary. It's a subtle shift from 'authentic frantic thoughts' to 'well-written frantic thoughts.' Some readers prefer the unfiltered version, arguing it's more immersive and true to a character under extreme stress. Others will appreciate the slightly more readable prose. It's a classic style-versus-substance debate, though here both versions have merit.
Think of it like a TV show. You wouldn't watch season 5 before season 2. The Hollows is a continuous story, not a bunch of standalone cases. Publication order is your viewing schedule.