I love Star Trek: Voyager. Each episode is a stand-alone, which gets resolved by the end of the 45 minutes. Every so often, I decide that I'd like to watch it, so I pick an episode at random to rewatch. And I always enjoy it immensely. In fact, the nostalgia I have for the show contributes to my newfound appreciation of the colorful family of characters and their relationships, so I think I enjoy it a little bit more now than when I first saw it. If I want fourty-five really fun minutes, that's where I head first.
I also love Battlestar Galactica. There are very few stand-alone episodes. Instead, each episode is just a small part of the larger story arc spanning the course of the entire series. I've tried to rewatch episodes, and it gets boring really quickly. It's hard to get really invested in a story when all the plot is just a development of previous themes, all the character development exists solely to move the characters to where you already know they'll be in future episodes, and there is no sense of closure. On rewatches, these episodes are very nearly worthless. On the other, I do enjoy rewatching the entire series, starting from the beginning, around once a year. That's rare enough that I'm not thinking ahead, so I can get caught up in the momentum of the character development. And by watching through the whole story, taken as a single entity, I get a satisfying experience where plotlines are introduced and resolved.
Neither of these two shows is as good as Babylon 5. (For that matter, I don't think any TV show is as good as Babylon 5.) It has a five-year story arc which puts BSG's to shame: While BSG's arc is constantly twisting in new directions, Babylon 5 knows exactly where it wants to be right from the beginning, and works its way there gradually. It is, as its creator J. Michael Straczynski put it, a novel written for television, with a clear beginning, middle and end. But alongside this long-term vision, each episode more or less stands on its own, no matter how critical a part of the arc it is. At the beginning of the episode, themes and plotlines are introduced. By the end of the fourty-five minutes, they are resolved. On rare occasions, I watch a whole string of B5 episodes to watch the arc unfold- it's quite a treat. But more often, I go back to rewatch just a single episode at random; at its end, I'm always satisfied. What keeps me watching is not the arc- that I only think about and admire later. No, what keeps me watching is the moment-to-moment greatness: comedy, tension, immediate problems.
It should be noted that B5 and BSG do not get better on rewatches as Voyager does. I have already identified the issue here as nostalgia. I am very nostalgic about Voyager, and not at all about either of my other favorite sci-fi shows. And I think I know why. Nostalgia is for the little things. You know what keeps drawing me back to Voyager? It's not the larger story- in fact, there isn't much in the way of a continuing arc. It's the family dynamic between the characters. Captain Janeway is the mother of the ship, Commander Chakotay is the father, the rest of the crew are the children, always spending time with each other, and Voyager is home. It doesn't need each story to radically change the status quo to earn such a special place in my heart- just this simple relationship. It is timeless and unforgettable. B5 has no such appeal, as the heavy arc progression overcomplicates. No simplicity, no nostalgia.
This is not to discredit long-term vision. An ongoing story is an admirable goal. It is enjoyable, even after having watched all of BSG, to just sit back and think about what's happened so far. It keeps the higher levels of the brain engaged, both by requiring memory and understanding of everything that's happened so far and by challenging the viewer to wonder what will happen next. The more popular reason given for long arcs is the added realism, but in my opinion realism is overrated. In any case, it is certainly a valid approach.
Now let's go back to the subjects of the title="The elusive key to longevity, Part 1">original question. Metroid Prime and its sequel Echoes break their world design into rooms, each one beautiful standing on its own. The rooms are not repeated; each is unique and remarkable in its own right. They have a mostly clear, linear path to follow through the very nonlinear worlds, so there is always short-term momentum. In addition, there are many platforming and action challenges, which by their nature are short-term entertainment. The layout is complex enough to challenge the player, but simple and elegant enough that he will remember it fondly. I have a lot of nostalgia for Tallon IV and Aether (the Metroid Prime worlds). As such, each time, in addition to the simple beauty of the world design there is an additional layer of enjoyment: the feeling of coming back home after a long period of time. This only gets greater with each subsequent playthrough.
The Legend of Zelda: The Wind Waker has an excellent and memorable story of the sort you'd find in a work of anime. It asks patience of the player, letting him know that the first two hours or so are merely set-up. It is not challenging. It is not satisfying in the short term. Instead, it uses its gameplay to craft a provocative story in the long term. Take the very first section, set on Link's home island of Outset. It sets up characters such as Link's sister and grandmother, it puts the plot in motion, yadda yadda yadda. But it doesn't give the player any hooks to keep him engaged. The gameplay consists of walking back and forth on the island. There is no tension, little humor, minimal emotion. It doesn't really feel like home (since running back and forth isn't all that welcoming), so that's no hook either. I'm not going to go through and analyze the entire game here, but suffice it to say that a large portion of the rest of the game shows the same disregard for the short term, instead focusing on a larger (twenty hours or so) story. TWW is not fun to replay.
Finally, The Legend of Zelda: Ocarina of Time. The best game ever made. It has an exciting story- though it's rooted in typical RPG cliché, it's told extraordinarily well, and with plenty of twists and turns. But at the same time, it always keeps the player focused on the present. What keeps me engaged from moment to moment is the emotion. The beginning at home, for instance, could stand on its own. Sure, it's teaching the player all the skills he'll need for the rest of the game, but at the same time there is the feeling of exploration and discovery, since the world design has intricacies such as hidden caves and a hard-to-reach ledge. There are things to find in every house. There is the welcoming feeling of being at home, as all the nearby characters make a point to say hello to you. There is the short-term game of finding both a sword and enough money to buy a shield. And there is the pressing plot point that the Great Deku Tree, for the first time, has summoned you to tell you something of vital importance. The player is kept entertained throughout. So while the game's complexity keeps the player from getting too nostalgic later (other than certain simple moments such as falling down a hole into a pool of water), the game stays fresh no matter how many times it is played.
In short, the key to longevity is simple, short-sighted, universal entertainment.