Most languages are "worth checking out." Every language offers something unique, by definition. The question is: which languages are "worthier" than others? Or, rather: how should you prioritise your learning queue?

I don't think the author's list provides much variation. They're all important languages, to be sure, but I believe you can get better mileage for your time.

My ten recommedations, in recommended order, are:

    - Racket (nee Scheme - why did they have to change the name!?)
    - Haskell
    - Java (reading the GoF)
    - C, and the POSIX libraries and system calls
    - Go
    - Javascript or Lua
    - Smalltalk or Squeak
    - Erlang
    - Forth
    - Prolog