The Best Christmas Ever - A noticeable change in the production values and tone of the show. I love the hand-held look that the more dramatic moments have. This is also one of the first episodes where I started to really *really* care about the characters. The image of the catatonic Bloberta is especially bold, and the final scene took my breath away.
Pleasure - I think this is one of the funniest episodes. Orel finds himself in a very complicated situation, which results in two dreams about God that are hilarious and adorable.
Nature - amazing for its *gradual* change in tone. At first it seems that the hunting trip from hell will be played for uncomfortable laughs, but by the time Orel says "I think you might be too drunk," it is apparent that they are going for something far more dramatic and affecting. Clay's drunken rant is downright horrifying and the interplay between the two characters is remarkable. I give credit to the beautiful animation and fantastic voice acting.
Numb - maybe the most all-around perfect episode. Every frame is beautifully composed, and the timing is spot-on. The lack of music (for the most part) makes the episode all the more stark. And the song that they DO use ("No Children") could not have been better. The last couple minutes are the most remarkable. We see that Bloberta reacts just a little to the news of Orel's being shot, and the transition between "You better go" to Clay's POV is great. And that final bit, with Clay hearing Bloberta and Orel and seeing her break down momentarily in the hallway, only to brush it away as the music strikes in... I can't remember the last time I saw something as powerful.
Grounded - also a very strong episode. I love that it balances some very funny and ridiculous moments with a hint at something deeper and more haunting. It works as a great complement to "Nature", showing that Orel is experiencing some kind of awakening, even if it has mostly been beat out of him. I also just love the way this episode moves. It is edited beautifully, with great timing. Not a second is wasted. I felt that the eleven minute running time caused some pacing issues with some other episodes ("God's Image", especially), but this works wonderfully.
Closeface - a dose of sweetness when it was needed most. After the intensely depressing "Help" and "Passing", this episode serves as a momentary release from all the tragedy. It focuses on my favorite relationships in the series - Orel and Stephanie, Orel and Christina, and Putty and Stephanie. The conversation between Putty and Stephanie is genuinely and unexpectedly moving. Even Stephanie is shocked at how sympathetic the reverend was. And oh my goodness, when Orel and Christina are dancing! It. Is. Great.
Sacrifice - the episode brings to mind a stage play like "Death of a Salesman". It wavers (sometimes almost imperceptibly) from comedy to tragedy and every line is solid. Scott Adsit gives a great PERFORMANCE (a word which is not attributed often enough to voice acting) here. This episode has so much weight to it, as it refers back to several other episodes, and only by watching the series in order can one appreciate just how powerful it is.
I'll agree with all of domrodrig's choices (except Christmas, but only because I haven't seen it since it came out). I also agree Numb was the most all-around perfect episode, and the POV scenes hit me too