Here are 3 articles about the game design:

#1 Codex Design: Cards and Gold As Resources
#2 Codex Design: Heroes and Tech Buildings
#3 Codex Design: Combat and the Patrol Zone

Here's a podcast about the design of Codex, what tradeoffs it gets to have by departing from standard CCGs, as well as some of the history about how the game used to be.

And here are articles about each hero and their associated spec. They are showing up in reverse order (sorry!) and it might help to read them starting with Anarchy, then Blood, etc.