One thing that has really been sticking with me about Dragon Age 2 has been (as is so often the case with Bioware titles) the relationships and personalities of your companions. Certainly, the arc of your hero is interesting, but it is the people around you that make it feel personal and compelling. DA2 does well enough in this that a few of your companions feel like they could be heroes (well, protagonists) of their own stories, yet this does not diminish your story in the least. Of course, the conceit that your story is being told by one of them does not hurt this perception.
Translating this to the tabletop is an interesting challenge for unexpected reasons. Certainly, there are lots of ways for a GM to make NPCs more compelling, and I’m all for those, but I don’t think they apply. It is far more apt to consider the other characters to be comparable to the other characters played by your fellow players.
Through that lens, the challenge is obvious: How can you create and encourage that kind of lateral play?
For all the reams of advice about players dealing with GMs and GMs dealing with players, there’s precious little about how to drive play between players. I suspect a lot of that is a result of game books being primarily written for GMs, and thus assuming the GM-Player dynamic out of habit. A few games address this, at least indirectly. One of the most subtle and brilliant rules in The Shadow of Yesterday is that you refresh your pools with certain types of actions, but those actions MUST be social in nature. Since everyone has the same pools, there’s a mechanical incentive to go do player-initiated stuff together.
Smallville deserves mention in this regard because I cannot think of another game where lateral connections are so essential. Relationships with other characters are an essential part of your character sheet. This is mighty stuff, but in some ways its _more_ of a solution than I’m looking for. I don’t want things to be quite that explicit, but at the same time I want character issues to be drivers of play with each other, at least occasionally.
Specifically, I love the idea that character A's issue creates play for Character B (and perhaps the whole group) rather than just being something that Character A deals with. Maybe this demands that issues come with an explicit "and here's the reason I can't deal with it myself". That's a good start, but I might go even further and find a way for character B to pursue the issue because it indirectly creates a problem for character A, if only because character B is distracted. Hard to do persuasively, though.
I am not entirely sure if this is possible, but it’s a problem I’m chewing on right now, and if nothing else, it’s producing some interesting flavors.