I voted 28+, but I'm pretty sure a fundamental issue here is what one means by "dungeon rooms", "continuous dungeon crawl", etc.. What is being critically distinguished from what else?
"Dungeon" in the D&D context is to me a functional rather than architectural term, and (rather obviously to the initiated) that function is not specifically to be a gaol (which is the usual meaning outside of fantasy games). The term "underworld" as used in OD&D, or "place of mystery" as in C&S, may be more suggestive. It need not be subterranean, or even indoors; an enchanted wood, for instance, might serve.
The key is that there are defined paths to explore, all (or at least most) leading to "adventure" of some sort. A small fortress, tomb, or other site that by construction or population is effectively a "gauntlet" fits a broad definition. However, a "proper" dungeon to my mind has the qualities of diversity that featured in the original D&D description; some amount of geographic scope is generally necessary to provide an ample basis.
The dungeon map is like a flow-chart, the transposition into physical space facilitating navigation of event "space" via an arbitrarily great number of possible paths. It is a way to "open up" a scenario. Instead of a script, you get something like a Rubik's Cube. There is not (necessarily) an arrow of time preventing the visiting of "paths not taken" previously.
One of several small dungeons, or part of a larger one, might offer little variety. It might cater to those who especially like tricks and traps; or fights; or exploration and mystery; or navigation of a social milieu; or some other limited aspect of adventure. In the broader scheme, though, variety is to be desired -- along with the ability of players to choose for themselves what they will undertake.
If one conceives of a D&D "dungeon" as categorically lacking one or another aspect, then naturally the want may exhaust interest (perhaps quite rapidly). Sameness in any respect tends to dullness. Even "empty" (of obvious peril and treasure) space can play a critical role in the rich structure of an engaging dungeon.
The assumption that an environment is to be of "one shot" utility, a puzzle to be solved, an obstacle to be cleared, seems par for the course these days. A more dynamic site facilitating reuse raises oft neglected design considerations.
"Killing things and taking their stuff" is an advertising slogan, not a prescription for getting "back to the dungeon" as it originally was conceived and captured imaginations.