First, there's this: http://thealexandrian.net/wordpress/36900/roleplaying-games/the-railroading-manifesto
It's serious stuff. There's several parts to that and as I begin writing this, I haven't even read them all. There's also this: http://thealexandrian.net/wordpress/5785/roleplaying-games/so-you-want-to-write-a-railroad
Which is very similar in feels, but actually a list of how to fail.
So, while Justin Alexander was writing these posts, I was reminded of the fact that +Donn Stroud told me I shouldn't listen to the 24th Episode of the Gaming & BS podcast, about Railroading and Sandboxes, because I'd have a rage anuerysm. I ran into +Sean P Kelley at GaryCon (over and over; great guy who I enjoy talking to) and mentioned this to him and he cracked up about it. (We had been talking about doing a DSR vs. Gaming & BS podcast and this or alignment emerged between Sean & I as the potential topic for the episode.) Anyway, you can find the episode here: http://gamingandbs.com/024/
I hope you don't have an anuerysm. As it turns out, I didn't. However, I've been thinking more and more about the Railroad and think I'd like to talk to you about it.
First off, and this is big, if you as the person running the game have any illusions that "the plot" of your game resides anywhere but in the course of action that your players take, you are flat wrong.
That is the number one mistake that I see DMs make: they get this idea that the awesome "plot" they're cooking up is somehow better or more important than what the players will and therefore take control away from their players. These DMs are wrong.
Some folks like to state that "a railroad ride ain't bad if the scenery is good." This, as well, is BS. It's effectively stating that a lie isn't a lie if you never get caught lying. Pretending to allow choice when you're really railroading just changes the flavor of the railroad. It's the artificial flavor of player agency. Not only is the DM doing this lying to his players, but he's lying to himself. Rather than getting better at encouraging player agency, the DM is just getting better at lying, distraction and manipulation. Sure those are useful tools in any DM's toolbox, but they're not genuine and the experience this liar DM is creating isn't authentic.
Justin's posts make a point of saying that the essence of the Railroad is not merely that only one course is available to players, but that players' choices are negated if they do not conform to the pre-determined course set by the DM. The second half of this is important because it's where the robbery of player agency occurs since the players have to choose from predetermined choices or risk irrelevancy. Having some things that are just going to occur (whether it's in the campaign background or foreground) isn't a railroad, but limiting the players' choices about how to react to or interact with those things, therein lies the Railroad. You've got to have the whole thing.
Because the plot resides in the PCs actions.
If you've defined what those actions are going to be and thus defined the plot, even if you've pulled off the "Great Railroad Lie" and people loved the scenery, you cannot touch the plain and simple fact that the plot of the game is, always is and always must be the result of the players' actions because the players are both actor and audience.
I know a lot of folks chafe when we start talking about the "story" in a game. I do, too. But it's difficult to use other words to talk about the overall course of the game. The "story" of the game isn't the backstory, it isn't the campaign demographics, it isn't the intricate web of deceit and lies the DM has woven between NPCs, it isn't the rules and it is only barely the adventures themselves. Instead, the actual story of your game is the one invented by your players as those players choose to act in the game world. This is the story, this is the plot. To constrain that is false and disingenuous and detrimental. To celebrate that fact, to encourage player agency, to offer more choices and get excited when players come up with things you'd never dreamed of, this is the art of DMing.
You are not a conductor, not a ticket-taker, not a travel agent and not a tour guide.
You are a possibility-maker, a dream-interpreter and an enigmatic story-shaman evoking the spirits of player agency to create something bigger than you could create on your own.