Aren't most of the AL adventures designed to be played in a single sitting? Because if that's the case, it is just not the same thing at all.
OotA is a sandbox adventure with an overarching plot running through it.
There are various events that are going to happen, and the players can jump from place to place in the sandbox with relative freedom until they pick up on what's happening (and then end up on their quest to solve the problem in the second half). That means that yes, you need to read chapter 2 to learn how to run the "we're walking through the Underdark from point A to point B" parts of the story, and you should probably have some vague idea of what can/will happen at the various places they might go. You don't need complete understanding of everything that happens at Gracklstugh until your players get there though, for example.
I admit, they probably could have done a better job of providing you with the "big picture" part first, as opposed to assuming you were just going to read the whole damn thing (well, more like "the whole damn half", since the first and second halves are pretty independent of each other), but all in all I think it works pretty well.
These ideas are at odds with one another.
What you're describing is not a sandbox. If all roads lead to Rome, no matter the choices of the PCs, it is not a sandbox. You've typed out all of the clues that it isn't a sandbox: "various events that are going to happen," "end up on their quest," "point A to point B," and "what can/will happen." None of these markers are elements of a sandbox. This is one of the differences between modules (mini-setting) and adventure (planned narrative) I was pointing out above. Mind you, NOTHING is ever pure sandbox or pure railroad; it's a sliding scale. But early modules were very far toward the sandbox side and this is clearly mush closer to the other from your description but with some strong sandbox elements or you wouldn't be calling it one, I am sure. Nevertheless, when the natural language you use to describe a sandbox are all elements of not-a-sandbox, it's clear what is being discussed.
On a different note, the idea that designers can't assume someone would "read the whole damn thing" before running it speaks to another point being discussed in this thread regarding attention spans. I cannot imagine someone buying a module/adventure and not reading it all AT LEAST once before attempting to run it. Reading it at last twice is the assumed norm, as well as spending time making notes (in it or on the side, perhaps in a GM's notebook), making player handouts like maps if not provided, putting together the necessary minis and terrain if you use such things, etc. GM's Day is a week from tomorrow and the ones who do the leg work are the ones who get the best GM's Day gifts!
Quite frankly, I want Dungeon magazine again. They gave you multiple adventures of various lengths in each issue. Heck, if they just scanned in all the old TSR-era issues and sold them in some pdf collections I'd be satisfied.
Sure, I'm more than willing to admit that OotA is not a pure sandbox. WotC doesn't do that. They craft an overall storyline for their various properties and the big adventure is designed to fit into that storyline. There are elements of them (especially in OotA) where the players have more agency than usual though, and things can play out in various ways which is why people refer to it as sandboxy.
Oh, don't get me wrong, I expect you'll at least want to skim through it before you start, but it's a 256 page book, expecting a detailed read of every part before playing the very beginning seems unreasonable to me. You're not going to retain it all anyway!
"Skim?" No. "Expecting a detailed read of every part before playing?" Yes. Of course. Retain it all? No, not a chance. No one equates reading with memorization or expects that. Folks that can memorize at a glance could actually get away with skimming. But absolutely "Yes," a GM is expected to have fully read and understood what they are going to run. Man, oh, man, this is what happens when the general gaming populace is led to believe that just any old person can GM a game. Yes, yes, I know. "Get off of my lawn" and blah, blah, blah, but GMing an RPG is not like officiating a minis skirmish game. It takes work, the least of which is reading the materials in advance. The LEAST of which. I can't believe this is even a conversation. I'll be back to this later but I have some stuff to prep for Gary Con next weekend My god! He'd be rolling over in his grave . . .![]()
Look, all I'm saying is that I don't think it's hugely important for the DM to be completely conversant (. . .)
Part of the problem here is that the word "Adventure" is kind of overloaded.
But hey, whatever helps you with feeling superior to the rest of us.
Do they need to have read in detail events that are going to happen 6 months from now? No. They don't. Heck, in some Adventure Path style campaigns it's possible that the stuff that's supposed to happen 6 months from now literally hasn't been published yet.