Well, it's possible that they actually manage to get a better story vs combat number ratio with this approach, assuming that each "cave exploration" has a story attached to it.
Generally, I'd like for them to have more "focused" adventurers. Allow the story, including twists and turns, unfold in less encounters. If they'd try to get something like a 3 act structure, each act should have no more than 2 encounters.
From a story perspective, fighting three encounters of undead to get to the evil cultists doesn't really add much. It is really just there to get you some XP and exercise your combat muscles.
Don't get me wrong. I really enjoy combats. But I would enjoy them more if there was a stronger narrative binding them together. Each combat has its own purpose in the story. If I need to find 4 McGuffins to achieve my next goal, don't give me 4 dungeons filled with monsters. Give me 4 encounters, one for each McGuffin. Or give me 4 adventures, with multiple NPCs and factions working together or against each other (or needed to change from doing the first to the former or vice versa, a mystery to be solved and so on), one for each McGuffin.
To go back to the first published 4E adventure, Keep on the Shadowfell.
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I might give them the 4 Kobold Encounters. They migh thave their purpose, because you have your Quest of stopping the Kobold Raids. The story isn't really that exciting and lacks a twist in the middle. The twist comes at the end, when we figure out that the Kobolds work for a Goblin who works for someone else.
The Dragon Burial encounter is pretty much inconsequential. Okay, you might fulfill a quest, but again, no real twists happening during that story.
Then, there is the Keep itself. Several encounters against Goblins, Undead and Hobgoblins and a few local monsters until you get to Kalarel. None of them really advance or twist the story, it is pretty straightforward. The adventure itself would be the same if you boil it down to an encounter against some Goblins at the start and some Hobgoblins at the end before reaching Kalarel.
The story of the slave traders has its appeal, but - it doesn't really lead to much into the adventure. The dungeon is essentially too big and too small at the same time - too many encounters, too little story advancement.
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Mind you, I have my own problems with getting this right when homebrewing. I have to work more on that, too.