I already see some good responses to your question.
As for me, before this course, learning a language was a mechanical process. I learn the syntax, learn some idioms and go with it. But, after this course, as the other commenter put it, I started learning every language as a set of features. That opens up a whole new world. For instance, when learning a new language, you seek out the features your are interested in and then figure out how that language lets you use it. For example, does a language support abstract data types, what paradigms of programming does it support, is it imperative or functional, lazy or strict, is the language supposed to be used as a bunch of statements or expressions, can common idioms be implemented as simple language functions or do I need the language to support it internally etc, does it support lambdas, does it do lexical or dynamic binding etc. The course also takes you through ML, Racket and Ruby and gradually exposes you through this concepts and in parallel explains what the trade-offs are as you give up once paradigm for another.
So, after the course, next time if you open up a beginners guide to any language, you will be seeking our answers to high level questions. The syntax to use will be learned automatically as you use those 'concepts'
Dan Grossman is a an excellent teacher. His passion for programming languages can be seen in his teachings. The homeworks are very relevant and helps you solidify the concepts. I am thankful to him for offering this course.
Hope this makes sense.