Having written so much code in AS3 I wanted to learn a similar language but that was simpler. Lighter. I had my own ideas of what I'd like in a language and I've found that Ruby has several of them. A simple example that stood out for me was defining a constant. In AS3 this requires a lot of typing that I felt could be implied.
public static const FIRST_NAME:String = "Javier"
In Ruby it's no different than declaring a variable but you type the name in all caps.
FIRST_NAME = "Javier"
Short and sweet. In another example I was impressed in how expressive Ruby can be. I had been figuring out the different ways I could repeat a string when I noticed in the documentation that operators were implemented as methods. Why can't I just multiply the string by the number of times I want to repeat it? For example:
"Ruby! " * 5
And that worked as expected! Simple things like this have made learning Ruby a joy.
Although I've written small scripts and re-written my site to learn Ruby I wanted something else that was structured. I had discovered two invaluable resources: Ruby Koans and Learning Ruby The Hard Way. While I'm half way through Learning Ruby The Hard Way I haven't enjoyed it as much as completing the Ruby Koans. The koans are a collection of units tests where you fill in the blanks or write scripts against pre-written unit tests. I don't remember ever learning a new language so much as I did by completing those koans. If you have any experience programming it is a great way to pick up Ruby fast.
If you have any resources you'd like to share I'd love to hear from you.