Interesting question roll vs role and I think one that can be a little problematic. Personally I prefer story over rules - which is why one of my favourite games of all time is Tribe 8. If you love a rich, detailed and thought provoking backstory I can heartily recommend this one (if you can still find it).
What it boils down to though, I think, is play style and group expectations. Fantomas mentioned earlier in the thread that I ran a very rules light game where people didn't even have character sheets till many sessions into the game. That was a lot of fun for me, but it is hard to keep going especially as some players started to feel directionless and uncertain of where they wanted to take their characters and the game as a whole. The problem there I think was that I didn't provide a rigid enough plot structure and the lack of rules didn't give the players a clear understanding of what they could and couldn't do. Instead they relied upon me to 'adjudicate' - and I'm sure that in some instances they felt I may have been unfair. But what this did give us was a greater feel for the characters and the plot. The players really owned who they were and the world that they were in.
At the moment I'm running Shadowrun and sticking as closely as I can to the rules (though not the background). I'd had a request for a greater level of character chance of death as some of my players felt that I was too easy on them and they didn't feel a sense of danger in encounters. Sticking to the combat rules makes it easy for me to kill off a character without being seen as arbitrary - I'm very careful to roll everything in the open and explain all adds/subtracts as I go. This helps them feel like their playing against the game as opposed to against me (it also helps that I don't cheer when the bad guys hurt them).
Mind you the only character to have been 'killed off' was actually handed to a slave trader as the group felt the character was too dangerous to have around
. What I'm finding with the more focused 'roll' playing is that the game has become more strategic and tactical in nature and more focused on the combat (which is now taking a lot longer to complete - sometimes multiple sessions) than the plot. Oh the plot is still there but it doesn't consume the same ratio of time that it did in my more open game.
I guess what I'm saying is that I can see the benefits of both types of games, I prefer one but injecting the other type is always good value and the real goal should be to achieve a balance that works for the group as a whole. At the end of the day the object is to have fun. I'll always lean towards the 'role' style of gameplay, but having a good mix of 'roll' in there can change up the gameplay and inject some spice as well.
When this becomes a problem is when you have a player or players who prefer rules based play, in a game where the GM is rules light and story focused. And vice versa of course. I've been in a few of these and it really comes down to how the GM and to a lesser extent the rest of the players handle the situation. As I said before, the aim is to have fun, and there's the old adage of a plan never surviving first contact with the enemy. Its like that with a game as well. The GM needs to adapt the game to suit the players and the players need to adapt to suit the GM and other players. Its when one or the other becomes inflexible that the game becomes unpleasant and not worth playing. Great advice? If only I could stick to it myself