I found them extremely accessible, and I was a high-school dropout. (Admittedly a very late dropout, but a dropout nonetheless.) That was back when volume 4 didn't even exist as listicles yet. And, let's face it, the sheer size (and cost) of the thing, even then, was a bit intimidating, but there's nothing in it that can't be followed with a bit of algebra and the barest hint of what the kids these days call "pre-calculus". While it may be a bit of a slog to listen to Knuth, his writing is about as clear as it ever gets, things are laid out in a clear progression, and nothing jumps out at you suddenly without a clear buildup and foundation.