Matt has done a great job of boiling down the essentials of the Ruby programming language. This is not a theory book, this is an - I'm an experienced programmer and I need to learn Ruby quickly book.
Once you get past the standard Hello World, he quickly jumps into variables, methods, interators, etc. These are the building blocks of the Ruby language and what sets it apart from other languages. All of these have simple examples that you can copy and paste into you own environment.
There are a lot of conventions in the Ruby language, like how methods are named and their behavior, if you have seen methods like 2.even? you have run across this. Matt goes through the common naming conventions for methods and what they mean. He brings difficult theoretical concepts like closures down to easily understood concepts. He also shows you how to use these in everyday programming. He then moves on into more difficult topics like meta programming.
If you are new to Ruby and want to learn it, this is a good place to start.