I just have to say how great a resource this is.
The approach they have is to have lessons before you do things in Hartl, which means you'll be more well grounded than someone going straight to Hartl. I've done some Hartl and after reading this, Odin Project really gets to the little parts and really compliments Hartl well. I would recommend doing their lessons in conjunction if possible. At least do Hartl, but using Odin Project as a companion to it, it's pretty lovely. Of course, based upon what one has done individually so far, a person may skip or already done some parts of what is asked in Odin.
Here is the full course page:
This is part of their larger Track 1 Curriculum, which has Web Dev 101, Ruby, and other courses.