Although there are so many outstanding episodes, especially in the 3rd & 4th seasons, I think that the episode that cemented my interest in the series and just totally blew me away has got the be "Z'Ha'Dum." The first time I saw it, I was completely blown away by it and successive viewings have not diminished, even in the slightest bit, the emotional impact of the episode. More importantly, it is a pivotal episode on which the entire rest of the series turns and JMS brings together several threads that were steadily built over the past two seasons and fundamentally and permanently reshapes our perceptions of the Vorlons, the Shadows, and what the Shadow War was REALLY about. What can I say about the acting? The acting was superb all around. The scenes involving Delenn dropping the snowglobe when Anna walks in unexpectedly, Sheridan's angry confrontation with Delenn about Anna, Delenn watching Sheridan's "good-bye" message, Sheridan's brazen(and suicidal) plan to crash the White Star into Z'Ha'Dum filled with thermonuclear explosives, and, of course, Sheridan's fateful jump into the pit (eerily reminiscent of the scene in "The Empire Strikes Back" where Luke makes the choice to jump rather than to join the Empire) as the Whitestar crashed were all perhaps some of the best moments in the entire series. If I could have any episode of Babylon 5 on DVD right now, it would be this one without a doubt. Superb from start to finish!