I more or less run only close-ended campaigns. When I first began playing RPGS ,the campaigns used to chug a long until we just got bored and stopped playing or our interest led us to other games.
When I ran The Enemy Within for WFRP, I kind of got a frame work as to how I like my campaigns to begin and end. Ending things well, has been a crucial component to all my campaigns.
I run all my campaigns in tv serial mode. For instance I may tell my crew that I am interested in running a campaign which would last for a couple of seasons -each season lasting about 12 sessions. If the players take to it then cool, if not we scrap the whole thing.
Running campaigns in this kind of serial nature allows me to intriduce story arcs, and concentrate on specific players each "season" or for a couple of episodes and allows the players to keep track of what is going on in the campaign. Everyone if they wanted to has a chance at the spotlight.
Now sometimes because I allow the players a lot of leway, and inject certain adventure ideas and plot points, the campaign may take a little longer to end, but that's cool, because everyone at the table knows it's going to end, and sometimes this fact imbues the sessions esp towards the end with a aura of urgency.
Also close ended campaigns work for me, because you can maintain the mystery of the adventures/setting long after the campaign has ended. By this I mean that there were other puzzles and strangeness in the setting that the players did not investigate because they were to busy accomplishing the goals of the campaign. These little pieces of atmosphere remain in the minds of the players long after the game has ended.
About the only drawback that I can think of at the moment, is that I sometimes feel, that the players do not have enough time to grow into their characters, esp if I place a time limit on how long the campaign will last. For longer term campaigns this is not a problem, but for campaigns lasting a brief period, my players have said that they feel they had not got a handle on their characters. This is why I still run close ended campaigns but the campaigns themselves last longer, in(my version of ) tv serial terms at least a minimum of 3 seasons.
Regards,
David R