I'll have to disagree with Perkins that these are individually satisfying adventure locations like traditional modules. Looking at something like Rime of the Frostmaiden, you have numerous locations that are 2-3 rooms in a dungeon with 1-2 encounters in it. Compare that to something like The Sunless Citadel, which has traps, monsters, factions, story, multiple levels, a memorable boss fight, etc. This was the stuff that we used to get in previous editions as a 32 page adventure.
Not only is The Sunless Citadel better than any of the side locations in Rime of the Frostmaiden, I'd go so far as to say (in my opinion), it's a better adventure than the climax of Rime, which essentially had one encounter worth fighting in the whole darned castle.
And I'm not trying to promote Sunless Citadel as the pinnacle of adventure design. It's merely above average, but compared to most of 5e's adventure design it's a masterpiece.