Well, depends.
So, here’s the key question: Do we look at Adventures in Forgotten Realms (AFR) as a part of Magic: the Gathering or do we look at it as a different game with the same set of rules? Wizards has officially stated that this set is not part of the larger MtG canon, so we might want to look at this set as it’s own independent game, like a precursor to the forthcoming Universes Beyond.
But let’s start with not doing that. Let’s commence with looking at AFR as a part of MtG’s larger ecosystem.
MtG is a game about dueling planeswalkers or, these days quite often, battling group of planeswalkers. These planeswalkers meet somewhere with their bag of tricks and fight it out over some unknown goals. In the early books, these were quite simplistic. The characters would just summon walls out of nowhere and so forth, but it all seems to have become more flavorful when the powerlevel of planeswalkers was brought down, and now there’s more of a feeling of two or more planeswalkers maneuvering to get an upper hand over their opponents.
There are things within the game that work against this, such as the powercreep that often form a shadow over the game, and the weird way planeswalkers have been introduced into the game as characters. (Why can I summon Ajani's Pridemate, when that should be Ajani’s thing?) Still, there have been a lot of places depicted in different ways during the games history and we shouldn’t forget that history either. Take Ixalan, for example. There were groups that were trying to reach The Golden City. In this context depicting certain places with the dungeon mechanic, but not others, even though those other places would make the whole thing feel much better from the flavor point of view, takes it’s own toll on the flavorfulness of the mechanic as well. Sure, they can’t go back and rewrite the history of the game, but at the same time that history comes with baggage they can’t just throw out either.
So, claiming that dungeons are good MtG flavor is wrong, but what about the other side of the coin.
Okay, it’s Dungeons and Dragons. There are plenty of dragons in the set (which mostly seem very forced flavorwise, but they are there), so we need to push dungeons in there as well, right? Well, no. As I’ve talked about previously, I don’t like how Wizards assumes that D&D players don’t have any sort of imagination and need to be force-fed everything.
But okay, Dungeons are a big thing in D&D or at least they seem to be (when I last played around a decade ago, we didn’t really go into any, because they really are not a big part of most well-prepared campaigns). So, they feel compelled to add them into the set. But what do they mean for the flavor of the actual games, not just the set. They are an interesting tactical and strategic choice. Which one you want to go into depends on what you need to happen right now, but also where you want to be in five or six turns. But that does not mean that they feel flavorful.
Suppose my Yuan-Ti Fang-Blade has just moved into the Sandfall Cell of Tomb of Annihilation. So, why did the Veteran Dungeoneer that moved into the Dark Pool at the Lost Mine of Phandelver have the option of blocking my creature? While dungeons might be a part of the name of the game, their existence is in no way flavorful. Are these creatures running around between these dungeons? Do they come back to the entrance after each venture into the next room?
They are flavorful only in the sense that they refer to the original material, so it’s basically just fan service and a very lazy kind of fan service. Not the kind that actually manages to use the idea in a meaningful and interesting way. It’s fine as a component of the game (although I think I’ll hate it on paper), but as flavor, it just sucks. It’s just imposing ideas from another property that don’t work the way you would like them to.