Clear, to the point, nice exercises, does not put on airs. Other "Scheme books" are really about something else. Eg, SICP (Structure and Interpretation of Computer Programs - 2nd Edition (MIT Electrical Engineering and Computer Science)) is an introduction to programming, which uses the "scheme machine" as the virtual hardware, and is not really a good introduction to the language (at MIT this was done in tutorials and through self-study). Various "Schemer" books (eg, The Little Schemer - 4th Edition) are more collections of puzzles, which I, personally, find rather annoying, since the authors DO tend to put on airs -- Scheme is just a programming language, don't make it sound like you are giving the proof of the Riemann Hypothesis.