I usually prefer to just make my way through primary texts, but I also realize the benefits of a well-crafted primer or secondary source review.

I think Kristeva's own "The System and the Speaking Subject" serves as a excellent starting point, but I can also recommend "Julia Kristeva" from the new Routledge Critical Thinkers series: Julia Kristeva by Noelle McAfee.

It offers an overview, context, and gets to the meat and terms of the work itself. Decently written, it is a quick read, so it allows you to catch the "lay of the land" before diving into such essential texts as "Revolution in Poetic Language."

What would you recommend?