There are two basic approaches to the early part of a D&D Hardcover Adventure.
The first introduces the main threat at the beginning and sets the party after it.
The other puts the main threat in the background and allows the party to discover it. Hoard of the Dragon Queen is the first part. You're thrown into the path of the Cult of the Dragon's plans, and the rest of the adventure is investigating what they're doing.Rise of Tiamat is then the fight against them with the knowledge of their goals.
— Merric Blackman (@MerricB) August 15, 2021
Rime of the Frostmaiden is more of the second type. You’re in a hostile environment affected by the villains, but you’re just trying to live your (adventuring) life there, not directly going after them until later. Likewise Out of the Abyss is the second type. You're adventuring through a hostile environment affected by the Demon Lords. It's only half-way through that the plot moves to "Let's stop them!"
— Merric Blackman (@MerricB) August 15, 2021
Tomb of Annihilation is the first type. You begin with the goal of “Stop the Death Curse”. It is quite possible that it would work better as the second type. You’re adventuring in Chult for a while, doing the hexcrawl exploration, and only later are asked to deal with the Curse. Princes of the Apocalypse is interesting. It's not quite either type, though it tends more towards the first. You have an initial goal: Find the Delegation. But you don't know who is behind it. OTOH, you're never just doing your own thing, it's always working against the cult.
— Merric Blackman (@MerricB) August 15, 2021
Curse of Strahd – when you don’t use Death House – is the first type. You very quickly are given the quest of “Stop Strahd”. (And it is very advisable to have the Foretelling very quickly so you know how!) Storm King's Thunder is the second type. You're adventuring through a land that has more and more giants in it. And then you get the quest. (Using a Great Upheaval makes it more type 1, but that's why I don't like it, because going from type 1->2 doesn't work).
— Merric Blackman (@MerricB) August 15, 2021
Dragon Heist is the second type. You're adventurers in Waterdeep. Parts of the main quest intrude on your adventuring life, but it's not until later that the main plot kicks into gear.
— Merric Blackman (@MerricB) August 15, 2021