For me it was the world building. The thought of a secret magical world that exists along side with ours in modern time sounded amazing.
But the World Building is no better than any books of the era. Indeed, there were plenty of other books that were far better world building around that same time. Like Wheel of Time has a far deeper, richer magic systems. His Dark Material is similar vibes and a far better magical systems. Others include The Magicians.
Yeah, even the Nikon 50mm 1.4D vs the 50mm 1.4G the difference in image quality is night and day. The D is also tiny compared to the G. Unfortunately, it’s a somewhat immutable fact of physics that good quality optics are big and heavy.