But it is not only here. Marvel Heroic Roleplaying's Breakout or Civil War follow just as direct a layout, even to the point of having the adventure's designers strongly suggest you kill off a major character in a particular Act. You see it in adventure design all over the place: Primeval has a multi-act adventure as its sample of play, pretty much any adventure that uses "acts" or "scenes" has this model. You can wander a bit in play, but in the end, you're at the end.
And frankly, I'm not all that juiced about that model any more, and I'll tell you why. Because ultimately you're just getting the GM's story. That isn't to say it isn't a good story, but ultimately you're just trying to figure out how to survive each encounter and move onto the next one. Which in turn puts pressure on the GM to build encounters that are survivable, because it wouldn't be much fun to not get to the end. So everything becomes a pretty set, structured mode of gameplay. 1, 2, and 3. Trying to go from 2 to 4 or F or whatever usually means a GM starts improving to the point where either you're steered back to 3 or had roadblocks thrown up until you backtrack to where you were before and try again to figure out what you should be doing.
And if you're a GM whose goal it is for your players to appreciate your cleverly crafted story, again that's fine, but understand that at this point I'm not invested as a GM in my own process anymore. Frankly, I find myself getting bored by my own creation, because I already know where it is going. I know how the evening will end. I'm just a character with a script who has practiced it time and time again. And at this point, I'd rather be entertained by the group as much as the group is entertained by me.
Which means, at this point, that I either need to become the most free-flowing creative mind out there, ready to just spin things off the top of my head, or I need to think about a sandbox.
Which brings me to my point. I use blogs to externally process (I'm an external processor by nature, I suspect) and I have been thinking a lot about the next game, and I've realized I don't want a campaign structure with a focus on "storytelling" in the way that the game is going to be "episodes" or any kind of layout where I know the ending. That means eschewing a lot of what is out there in game design, but I think for the sake of my own engagement and interest, this is the best way.
Now I know there is a lot of information and advice about building sandboxes out there, and I'll be processing some of that here. Stay tuned.