Poor word choice on my part, it is that they felt big and empty compared to old school dungeons which had some many creatures and traps jammed into them that they became the subject of parody.
That map above looks like one where a party could get seriously lost in. I wonder how would one implement that on a VTT?
If you look at level 10 in Dungeon of the Mad Mage: "Murial's Gauntlet" over half the rooms are empty and most of the encounters are speed bumps for a level 11 party. I had to reinforce the drow heavily. I will admit that I messed up running Murial though.
Probably would help if more potions and trinkets were scattered about.
There's an interesting variation in people's perceptions of how crowded or empty old school dungeons were depending on which old school products they look at and what their own DM's style was.
The original OD&D guidelines recommended a LOT of empty space, with only about 20% of rooms and chambers supposed to have monsters in them (not counting wandering monsters). If you look at Expedition to the Barrier Peaks, or the couple rare images of level 1 of Gygax's Castle Greyhawk which folks have passed around and pored over for some years, you'll see that they follow this guideline. You actually see the facing key page for the latter in the photo, and something in the neighborhood of 120 rooms out of 160 don't have a key code at all- totally devoid of description or contents in the key. This is also part of why I often recommend that modern DMs use Dyson Logos' updated triangular cross-section maps for Expedition rather than the original circular ones- they cut out a ton of "dead" space.
A big part of the original playstyle was navigating the dungeon, with mapping, resource (torches) and time management, being skills tested. Trying to avoid getting lost, trying to find hidden treasures without running into too many monsters, figuring out spots where it made sense to devote time to searches and risk more wandering monsters, etc. Dungeons with lots of empty space have greater verisimilitude from the perspective of having actual buffer space between monster lairs so it doesn't look like they would necessarily have killed each other before the PCs got there or be allies like you would assume if they live next door. They also give players the option to run away from and then maneuver AROUND a monster lair that looks too tough.
Tournament modules, OTOH, often had more dense content in part due to time concerns in limited duration convention play slots, and published designs were often much more dense than the original guidelines for similar reasons- players largely seemed to prefer hitting more monsters quicker, less maneuvering around empty rooms. There's a dramatic demonstration of this contrast between Mike Carr's B1 In Search of the Unknown and Gygax's B2 Keep on the Borderlands. Mike Carr's module is much more about exploring this weird, mostly empty, mysterious space, where the Caves of Chaos has all these lairs right next to each other.
Speaking of getting lost, one of the standout experiences I had over the last year+ of playing old school games online with remote strangers was playing in a "proper" megadungeon execution of Stonehell. The DM used theater of the mind combat and a single token for the party maneuvering on the map using 10' squares. He used dynamic lighting rather than Fog of War on Roll20, and the dungeon is BIG. So with 10' squares and 30' torch radius, we're looking at a visible area of 7 squares across, and mapping being actually very important to not get lost. We had a risky delve at one point down to a lower level and unfortunately wandered into an evil crypt that was one of the more dangerous spots, and woke up a Wraith. We fled post-haste and unfortunately had been a bit loose in our mapping, taking a wrong turn on the way out and being caught by the wraith. We got lucky that only one person got drained, and it was a really eye-opening glimpse into that part of old school play.
