They just added all those new rules from the codex update to the codex, and did some minor changes compared to the PDF version - e.g. hellion aren't forced to fall back anymore if you don't want them to leave close combat, some point costs got adjusted. All changes compared to the PDF version are in favour of the DE player.
There is no new fluff though, they even took that story about the intentions of the incubi and about the Dark Father out of the codex, in order to gain space for the additions.
jwu
