Continuing from The Little Schemer, this one has mutable state, closures, memoization, Church encoding, vague allusions to Leibniz's Law, cycle detection with the Tortoise and Hare algorithm, generators implemented with continuations, and other fancy ideas in programming. But it doesn't actually bother to use the conventional terms for the ideas; oh no, that'd be too straightforward, so the words "memoization", "closure", "Church encoding", etc. never appear in the text. Ugh. This is a completely irresponsible way to teach Lisp/Scheme, and it's this kind of nonsense that helps create the "smug lisp weenie" stereotype. If the material seems hard it's because the authors are being coy with their explanations.
Fun for review if you already understand the ideas, but I think The Seasoned Schemer does a disservice to anyone trying to learn something new.