My game concentrates on character building over world building. The idea is that given a general premise covering the general types of things the characters will be doing in the game, and how, and a vague setting, the players create this fantastic cast of characters and the GM wings the story in response to the motivations and goals that drive the characters.
This is all well and good, except for the bolded part. Its easier said than done. What I have so far are the types of characterization I would like the players to come up with, what they represent and why they are important, and multiple examples of each. Although not available for download, Ive also come up with a playable canned scenario with pre-generated PCs and NPCs as a complete "this is how I see it" example.
However, even assuming the players understand what the game requires, there is no guarentee they can come up with something good on the spot. BE CREATIVE NOW! is a little like the 'and then magic happens' part of a process diagram. Some players might revel in that kind of thing (like me), while a lot of others will be saying "this is taking for ages, and I cant think of anything!"
I leave the option for the player to fill the "characterization" in as they go along, but because it dosnt have as much direct impact on the play as say, a trait that you can use, it tends to get left at the station.
I have more to say, but Id be interested in peoples thoughts about this. I guess its a kind of general thing for RPGs but because my game is tagreting characterization so specifically, its a big issue.