Whoever Did This
There is something about the staging and filming of the disposal of Ralph by Tony and Chrissy that is truly unique in terms of the tone and atmosphere--something that NO other episode of The Sopranos has.
The latter half of Whoever Did This almost feels like a different show in terms of it's feel and tenor.
The lighting and color timing subtly shifts after Ralph breathes his last, and it's a look unique to this episode and this episode alone.
There is the near total absence of sound whatsoever; the sequence feels not only like a proper movie, but a *silent* movie. Only Tony's own killing of Christopher in "Kennedy and Heidi" approaches the sequence in terms of how low-key it is, and the later scene lasts all of five minutes, if that. There is also something almost supernatural about the atmosphere. For instance, Tony, Chrissy, and the audience are suddenly startled by a thumping sound downstairs while they're in the bathroom which is soon revealed to be ostensibly just the bowling ball rolling down the basement stairs. But in the moment, it feels as if Tony and Chrissy are in a haunted house and the thumping/rolling sound is that of a ghost making it's presence known.
Someone else here on reddit pointed out that the dialogue between Tony and Christopher in the sequence is like something out of a Samuel Beckett play.
And this review https://sopranosautopsy.com/season-4-2/whoever-did-this-4-09/ sited elsewhere, compares--not entirely inaccurately--the "disappearing" of Ralph's remains to the works of Poe and Dickens.
There is also, of course, the constant threat of Tony and Chrissy being caught in the act.
And I suppose that Tony knows on some level that he has crossed the line and is now sailing into uncharted territory. He knows he has just killed a made man, and a capo no less, without having a sit-down first or a valid reason or excuse. It is the only murder Tony commits in the entire series in which he is motivated by pure rage and nothing else, as well as the only murder--apart from Chrissy's own--that he commits on the spur of the moment and with his bare hands.
The subdued, eerie atmosphere is enhanced by Tony and Chrissy's manner of comporting themselves--Chrissy is high as a kite on heroin, while Tony seems like he's either hungover or recovering from the flu(what is that about by the way? His injuries from the fight? Emotional exhaustion after what he's been through what with losing Pie O My and working himself into the rage needed to kill Ralph? Knowing he has crossed the line as mentioned above?)
And then there is of course, the way Tony wakes up at the Bing a few hours later to discover Christopher gone, Tracee gazing at him through her photo on the mirror of the dressing room, the empty stage Tony walks past as he calls out Christopher's name, and the strangely paranormal-looking bright light Tony walks into afterward that just might be Tracee's ghost newly freed from where she was killed now that she's been avenged, as Michael Imperioli suggested on the Talking Sopranos podcast.