Functional programming/paradigm. It's a pretty nice language to learn it (my intention was to learn Clojure, but I read this book first so that I had an small base).
But today, one can learn functional programming also with other languages than Lisp.
The book isn't really about lisp, it's about thinking in terms of higher order functions and recursion, which apply in any functional language.
Which is also brilliant, but is more about thinking in terms of types (more advanced type systems, then C/C++/Java etc).
Should make a good warm up for learning the likes of OCaml and Haskell
Almost all the exercises can be done in Haskell with a small amount of syntactic adjustment
The cool thing about learning in Lisp (or Scheme) is that the language doesn't really get in the way. It's less about learning the syntax of a language and more about focusing on the algorithms/concepts.
For instance, it's a great manifestation of lambda calculus.