It's true that HTDP is a little slow, but Felleisen is a master of CS pedagogy, and it shows in the book. The "design recipe" system that the book presents is actually extremely helpful in designing software once internalized. HTDP and SICP are in my opinion rather complimentary--I worked through HTDP in a couple weeks and am still working through SICP when possible. I consider the background that HTDP has given me valuable, not only as a Scheme programmer, but as a programmer in general.