Was scared by the Udacity course at first, but once I got started, I felt capable. Now that I've been in it a while, I am bored. Learning without "doing." I liked the Bonfires which felt more like "work" rather than "lessons." Udacity is way better than Codecademy though. Well built, alive-feeling.
Others:
- Have read 68% of Kindle Joomla 3 Explained (2nd Edition), by Stephen Burge, from Joomla Press. (Published August 7, 2014. Doesn't cover new Joomla 3.4 release.) Also slightly boring, but a necessary orientation.