I'm a passionate pen & paper role-player and have been for about fifteen years (with a rather long interruption in active play)/ a bit more than half my life now. I started out around 7th grade in a traditional group of misfits pen&paperin' it up trying to level their ill-conceived DSA (Das Schwarze Auge, the earliest German spin on the fantasy-level-grinding RPG type that DnD invented) characters through a string of loosely connected adventures GMed by the one amongst us with the least imagination. It wasn't pretty and after it all sort of stopped happening I didn't play until university. As we have an on-campus role-playing society, it was easy to find like-minded people there and I started enjoying the weekly gaming-session on campus every Wednesday, with two bi-weekly groups each semester, which also led to private gaming-sessions on an almost weekly basis. Good times. The topic of this post, however is a different one: The different flavor of adventure to be had simply by differentiating narrative length.
As a disclaimer I'll say that pen & paper RPing is a diverse field and I'm aware of that. There are the classic dungeon-crawling kind, the abstract kind where multiple people may play only two characters in a set amount of scenes without a game-master and anything in between. As I'm more into the classic variety of the DnD-ilk (although I have only played actual DnD once) but with more role-playing and a little less dungeon-crawling/monster-slaying than that may imply, the observations in this post will be about games that are actually designed with the option of a long-term campaign. If a game is made to play out the final three days of a set number of protagonists and how they all kill each other over a relationship-drama (looking at you, Fiasco!), it's obviously out of the question for a year-long campaign (although I in no way discourage anyone from playing those. They are simply not my topic today).
So, extensive research (thinking of my past years of gaming-experience) has led me to believe that the Domain of gaming in which we are going along the branch of the Kingdom of table-top gaming towards the Phylum of Character-Play leading to the Class of Pen&Paper-RPG contains in the Order of GM-narrated RPGs a wide variety of game-modes, which can be classified into One-Shots and Campaigns, respectively. Campaigns are divided into three different play-modes and generally consist of a somewhat samey-party of players either: Playing a long-term story that the GM has thought up (or read up), leading to a final confrontation or somesuch finale that ends the story somewhere; several shorter stories (as in a series of unrelated adventures) that the characters stumble into/seek out, each ending at a point before another kicks in (some leaving the game-world with permanent fixtures such as recurring NPCs, locations or artifacts); or it's a sandbox, where the GM only makes up the world and the players fully decide what to do in it and all the GM has to do is make up a way the world reacts to it (and thus doesn't have to prepare a whole lot). These three types of campaign can of course have rather blurry boundaries between them or one may lead to another. Then there are One-Shots, usually designed for being played in one session of gaming (often at conventions with strangers).
Interestingly, from a narrative stand-point long-term campaigns containing a single overarching plot have more in common with the short One-Shots than the other two brands of campaigns. Their two great common denominators are an overarching story containing the same group of people and, most importantly, them actually ending. Now a good One-Shot requires the GM to be well prepared or very creative and disciplined. While you can make up a good story on the fly, it's hard to get it to an actual ending-point within a set amount of time if you haven't planned ahead. The great advantage a good One-Shot hosted by a well prepared GM has is probably the tight and dense story-telling. A long-term campaign leaves a lot of room for side-questing and banter, but it is also in danger of getting off the focus and mucking about. The great advantage a long-term campaign has in my opinion is the growth of the characters, not only in personal development, but also in relationships with each other (if you have players interested in actual RPing) and also, for some a very important fixture, in numerical stats (for players less into RPing and more into RMing - RuleMongering). Games with an experience-system of character growth will usually lack any upgrading within the confines of a One-Shot, while they mostly require it for the final confrontation after a long campaign.
Now there isn't really a competition between One-Shot-Adventures and long-term Campaigns, as both are very different formats for different settings of players getting together. Time and regularity of meeting up are important factors and as such, the two are not interchangeable. The crux lies more in the choice of long-term game-type. If you intend to play for however long your group still lives in the same city while living out ever-increasing power-fantasies, a string-of-adventures type of campaign may be for you. A great overarching-story-campaign is the right choice for those who want epic adventure but also want a grand-fucking-finale in the end, where their character-arcs come down (as arcs are supposed to) and everything finishes off one way or another (which is something I immensely enjoy, even if it leaves a character I've played for two years dead on the ground of the arch-nemesis' throne-room). If your GM is lazy (or you are a lazy GM), then the sandbox is your thing: A creative GM can make up the world and adventures taking place in it along the way, as the players go, the GM creates the world around them. It definitely needs less preparation.
As I like GMing a lot but own no actual rulebooks, I have always made up my own game-systems for specific settings and have GMed all of the above play-styles, sometimes jumping back-and-forth between the different long-term modes. Now the interesting thing is when you pace the same adventure in different ways. I once GMed a One-Shot, which our weekly gaming group spontaneously needed because a crucial player of our regular campaign was missing that night and I said "Hey, I have this vampire-hunt at the ready...". It was a rather dense little adventure about a group of vampire hunters in the year 1900, traveling to a small logging-town in the woods due to a letter sent to their secret society by a local churchman, encountering a total of five vampires of different might. The game, which I intend to fix up for a proper release some day, is designed to be radically asymmetric gameplay, the group of fragile human player-characters unable to best any of the vampires in an open fight, having to outwit them and catch them off-guard (like, during the day. Duh.). The group went through the adventure in five hours, destroying all of the vampires but one, whilst losing no PCs themselves. A year alter I set up the same adventure as a campaign for a semester of bi-weekly play in our university-gaming-group. As usual with a larger group of players (and the high interest in the game lead to eight players sitting at the table), the game was much less focused and despite the game containing the same set-up, the same set-pieces and the same in-game number of days/nights passing until the finale, it took sessions amounting up to about 35 hours of play-time for the group to finish the adventure (and failling to kill boss vampire and all but two of them dying). So the lesson?
Pacing is what the GM and the players make of it...