This episode gets highest marks from me for three reasons:
First, the performances and characters are just fantastic. This series often suffers from excessive overacting and watery-thin characterization; you'll find neither in this episode. Our two lead actors are skillful enough to let you know exactly who their characters are from the get-go, and every line delivery feels like a real person. It helps that they're both entertaining and have an "odd couple" thing happening that make them fun to watch.
Second, the story itself is simple, yet completely enthralling and builds in tension. It's mostly two men in a room together while one bargains for his future, and it is a thrill to watch.
Third, I had no idea how it would end, right up until the last second. That's rare for me when it comes to this show -- I'm too familiar with the Hitchcockian "twist ending" to be caught by surprise. The performances here give so much complexity to their characters that I honestly couldn't tell who could be trusted and what their decisions would be.
No spoilers here, so I'll just say that the ending actually made me gasp. It was perfect.