Though we are not yet at the climax, this episode stands out because it is a Format Breaker. Yes, there is a killer of the week, but it's not an isolated case and the way it connects to the big picture is handled really well. Criminal Minds has rarely been this captivating, their opponent so compelling. We get new information and twists at a steady feed, plus genuine shocks, the biggest of which is pretty hard to see coming. From script to the final product, all is great. There is even a firefight that is reminiscent of Michael Mann's classic Heat, and, unlike in most other cases that recall Heat, this firefight does not come across as a botched homage or imitation.
So why not more than an 8/10? Well, the story hasn't climaxed yet and there really is nothing *exceptional* here, "only" solid craftsmanship. Also, the whole "the Secret Past of Emily Prentiss" idea is still Retconning, no matter how well done. And master storytellers do not resort to Retconning - they plan everything *in advance*. Yes, in American TV this sadly often leads to potential left unrealized as shows planned to run 3 to 5 years are canceled after Season 1 (see Invasion, FlashForward, The Event, etc.)... but *the fact* remains. That being said, one cannot wait for the climax episode.