After running a few multi-year campaigns that were enjoyable but draining, I've come up with a different approach for the next year or so. A series of four-session long adventures, with each adventure set in a different genre and with a different mix of players.
The first adventure was a lot of fun and definitely a chance to trying something different: a Western! I used a free D20 RPG called Go Fer Yer Gun! and while it might not stand up to campaign play, it was perfect for four sessions of gunslinging. The PCs arrived in the veritable ghost town of Silver Gulch (nearly abandoned since the local mine petered out) and soon got caught up in a scheme by a mysterious masked bandit to drive the remaining townspeople away. It was a chance to use all of the hallmarks of the genre, including cattle stampedes, a "new sheriff in town", abandoned mine shafts, and even a damsel in distress about to be blown to smithereens by dynamite! We had an interesting mix of PCs: a Maverick named Dusty (who ended up becoming the new sheriff after the NPC sheriff was killed at the beginning of the adventure), a Drifter named Quint (who had a predilection for shooting villains in the back), a female Doctor named Zenobia (a no-nonsense type), and another Doctor named Doc (a scarred fellow). Naturally, they managed to save the day after an exciting climax on a teetering rope bridge high above a gulch and unmask the bandit leader as the town's mayor! I stole a good chunk of the setting and NPCs for the adventure from a Western novel called "Ghost Town" by Will Sutton, and it really helped me flesh out characters.
The second adventure will start up in January and will be a 1930s pulp adventure in the Indiana Jones/The Mummy/Sky Captain and the World of Tomorrow vein. I've still got a lot of details to work out, but I'll be using the Savage Worlds rule-set for the first time.
Then later in 2016, I've got post-apocalyptic mutants lined up (using Gamma World) and super heroes (not sure what I'll use yet).
We'll see how the experiment proceeds, but so far it's been a refreshing way to move beyond the standard sword and sorcery and try out some different types of RPGs.