So if I was going to run a Wörld of Metal campaign... here is one idea for how to do it. This would work pretty well sitting around a tabletop but it is really well-suited to an online Google+ game with a fluid playerbase.
1. One week (or more?) before each session, I pick one of the players at random to be the party leader. If we're on G+ then it's their job to pick a time and assemble whatever other FLAILSNAILS players they can get.
2. In addition, the leader has to choose a metal album that will form the seed for the adventure.
3. If they want, they can also pick which region they want to go to. If not, the region will be the same genre as the adventure seed. (This is mainly so that you can visit the Land of NSBM without actually having to listen to NSBM, because fuck that.)
4. I will write an adventure based on the album. This may involve repeated listens to fully understand the album's lyrical themes or I may just look at the cover and take a good guess.
5. When we start playing, any form of travel is handwaved immediately. If the last session was in the far western isles and the next one is in psuedo-Japan, I will just say "Well, you spend about three years travelling across the continent, having many adventures along the way. No, they don't give you any XP." Think of each session as a different sword & sorcery story; Fritz Leiber and Robert E. Howard* never felt the need to document every last detail of the characters' travels from one adventure to the other.
6. Of course this structure is flexible. If the adventure takes more than one session to run then the players can stay in the same place. If they start generating their own objectives then they can do that also.
The advantages of this system would be that it would be relatively low-prep, and the prep would come at a steady pace rather than frontloaded. I would try to make the adventures open-ended and interesting, but the fact that the players themselves picked the adventure (in a sense) means they are motivated to engage with it. And the one-session time limit could (maybe) encourage forwardness rather than dithering. I think this system works particularly well for the Wörld of Metal because the setting is very big but it only really works if you get to experience many different parts of it. If the whole campaign was stuck solely in the Land of Death Metal, then it wouldn't be engaging with what makes the setting cool.
The main disadvantage would be that outside the adventure locations, the rest of the world is fairly empty and/or handwavy. The players don't get much choice about which adventure hooks they engage with. On the other hand, the details of the world would get more fleshed out with each session we played.
*Probably. I've never read any of the original Conan stories, so I'm guessing based on the Robert Jordan ones.