So, about the title of the album. It seems we are back to the Kabbalah. As far as I know, Sitra Ahra (also spelled Sitra Achra) means "The other side". It is supposed to be the entity from which all evil emanates according to the Zohar. It is one of the controversial manifestations of Kabbalistic duality (which is usually seen as a monotheistic net of knowledge). It is also supposed to have some connection with free-will, or at least the gift of free-will is supposed to be the reason why there is evil in the world.
The Sitra Ahra may be a metaphor for the left-hand path of philosophy, in my opinion (but we never know what's coming from Therion, I'm just sharing a very raw interpretation!).
Wikipedia, for instance, has some information on it

I'm expecting great things from both Therion and Thomas Karlsson.
And I hope we have at least one Lovecraft-themed song.