Damn that was a good episode. So much in the way of wonderful content, dialogue and the ending music piece/transformation legit gave me chills.
If I had to pick one specific thing that really stuck with me it was how gloriously unsettling Cell was in this. While his Perfect form has certainly been menacing or creepy at points he was more aimed towards humour.
But this episode masterfully takes all the characterisation Perfect Cell has built up over previous episodes, keeps it, yet tilts the perspective just a little to the right and in doing so brings Cell to depths of creepy-evil we haven't seen since his Imperfect Form days.
The increasingly not okay fixation on Gohan, sense of honest to god malice/sadism he displays throughout the torture session ie his taking the Senzu Beans away just after Goku works his way to a "My God What Have I Done" moment, the Cell Junior's who from birth to naming to beat down work.
This episode is both the point Gohan steps into the hero role in the most epic way possible and the point where we see Cell as the villain in all it's terrible glory.