All the previous episodes of 'Law and Order: Criminal Intent' are in my opinion very good to outstanding, such a promising standard for so early on which one doesn't always get with shows but it has certainly not been unheard of. Which range from great from the get go, solid but a little unsettled but gets better and doesn't ever take off. "The Faithful" and "Jones" to me were the standouts as far as the previous episodes go.
"Enemy Within" is one of the weaker episodes of the ten (including this) up to this point of the season, and show, but is still a very good one with a lot of fantastic things. While just missing the extra something of the best episodes, which have more tension, more of the shock factor and are a little more complex in the storytelling. There is not really much inherently wrong with "Enemy Within", other episodes just executed a few of their components better that's all.
It has plenty to keep one going, though despite there being no shortage of suspects there was little doubt in my mind about which side of properly innocent or guilty the prime suspect was, their actions though are questionable and it is not a surprise as to why they're suspected, and guessed the identity of the culprit correctly quite quickly. Though the overall final solution was a little more surprising.
Despite being surprising certainly, a few of the motives of the suspects and how they act are a touch extreme, like for the prime suspect.
There is very little wrong otherwise though. The production values are slick as always and the music (though there is a preference for the other 'Law and Order' themes) isn't overdone in orchestration or how it's used. The writing is never simplistic or convoluted and respects the viewer, and the story has a lot of twists and surprises without feeling too many or muddled.
Vincent D'Onofrio expertly brings out Goren's somewhat eccentric and hard-boiled edge, beautifully matched by a more subtle Kathryn Erbe. Their chemistry carries the episode very well. The investigative elements and methods the detectives use in solving the case are fascinating.
Concluding, very good. 8/10