A recurring discussion in MV circles (and I bet various other popular subgenre forums) is the definition itself and whether or not game x or y fits within it completely, partially or not at all. Let's start with a basic definition:

A Metroidvania, also known as a Platform Adventure, is a subgenre of Action Adventure and Platform games. In short, these are real-time games that focus on platforming, exploration, gradually making the player character better able to traverse the world that they're exploring by acquiring various upgrades, and (usually light) puzzle solving. They feature interconnected worlds with some degree of persistency, that is gated in content by persistent abilities or tools acquired by the player (as opposed to just keys, non tool/ability-based puzzles or combat) and which gradually opens up more as the player overcomes its obstacles. Generally these games have some degree of non-linear progression while subtly guiding the player towards the next intended path, and to some extent a "loopback" structure where the player happens upon ability gates that they'll come back to later on to progress. Historically they have been side-scrolling and in 2D but they can be third-person or first-person and in 3D as well.

Today we're looking at Elder Scrolls II: Daggerfall (PC, 1996), more precisly the Unity ver. and its opportunities for modding. It is an Open World RPG with real-time movement and combat, and a Dungeon Crawler RPG. Some call it a Fantasy Life Sim. I'll go ahead and make the case for and against it as a MV:

For:

-Movement abilities like jumping and flexible climbing including jumping between walls (you can climb any wall and turn around while clinging to a wall), swimming, upgradeable running speed and jump length+height, as well as glide jumping and flight via spells. Invisibility and stealth can be considered traversal abilities, and torches too if you use mods to make them important.

Out of these only climbing is mandatory but you'll probably want to use flight and glide jumping, as well as spells for faster swimming or underwater breathing for shortcuts, additional loot and convenience. Gliding or flight are also good for avoiding fall damage. Your movement abilities also let you explore where enemies are too tough to fight as you can run past them and generally shake them after a while

-Some backtracking into previous dungeons to progress

-Both the main quest chain(s) and the side questing are non-linear

-Some town-like locations within dungeons and some of the town castles connect to a dungeon

-While not a requirement for MVs it has a detailed map feature that lets you place markers in dungeons and town buildings. There's also various forms of fast travel including a teleport beacon spell. Info mode also helps with directions as you can look at a building from far away and have the game identify it for you

-Some decent switch and spatial awareness puzzles

Against:

-Dungeons are not persistent so the enemies and puzzles reset even for the handmade quest dungeons when they're exited (and the layouts for the rest), however there is a persistent dungeons mod that changes this

-Outdoors gameplay is not very interesting from a movement perspective besides climbing or flying to break into walled off towns at night and escaping from guards if you're a thief, though are are mods that can make the wilderness more interesting

-Overworld and dungeons structure and you generally don't backtrack into the latter. Furthermore, when you do it's not because a new movement ability lets you progress further but because you have a new quest item to deliver and/or an NPC called for you. You can actually gain access to the aforementioned spells related to movement abilities very early in the game, by joining a mage guild and buying or crafting the spells, and climbing and jumping are abilities that you have from the get go. You're just gonna be worse at using them as the game employs a use-based leveling system. This can't be modded, currently

-Some dungeons aren't really designed with the movement abilities in mind and most have an abundance of corridors for fighting monsters in. This aspect also can't be modded (yet)

-Time limits on most quests though they can be removed with a mod

-While some dungeons have more than one entrance, they all lead to the same place inside

-No real bosses if you care about that, just stronger versions of monsters for some quests

In conclusion, Daggerfall has decent appeal to MV fans, particularly when modded. However, the open world and leveling systems go against the more strictly structured nature of MVs. With the current terminology, it can be called a MV-lite, or an Open World MV.

This is more of a list post. I'll go by the points below as a definition and comment on each element individually:

-Higher than average difficulty - This is as old as games but if we include a boss focus, I suppose Ninja Gaiden, Ghouls 'n Ghosts, Shinobi, Castlevania and the like are good early-ish examples.

-ARPG w/ character creation, shops and leveling - Well this one goes far back. In Japan there's games like Dragon Slayer and Hydlide from 1984, which took their first steps into 3D with WibArm from 1986, but JP real-time/action RPGs didn't tend to have character creation (Hydlide 2-3 are an exception). In the west there's Dungeon Master from 1987 for a semi-3D one.

-Heavily interconnected and usually non-linear world - Some have tied this to Metroid but I haven't seen the developers of the Souls series mention it, so not sure. There could also be a connection to King's Field and from it to Ultima Underworld, which is one large underground maze from what I've seen. Or to Zelda 1 but that game has a clear overworld and dungeons split.

-Corpse runs - Probably influenced by Diablo and/or World of Warcraft (though Everquest predates WoW and also had it)

-A checkpoint system to replenish health and respawn enemies - Not sure, but System Shock 1 does a similar thing via its restoration bays which resurrect you after activation.

-Storytelling via pieces of lore found through items in the environment - This seems to originate from text adventures going back to Zork, but the first action game I know of is Project Firestart (1989). DS or King's Field might've gotten it from Ultima Underworld.

-Stamina bar - The now obscure action games Legendary Axe and Astyanax from the 80s use it for combat in the same way. The first japanese ARPG I can think of to use it is Seiken Densetsu/FF Adventure for GB (1991). But it's also an old (W)RPG element, where it works differently as it tends not to regenerate on its own and was initially used in turn-based games. The oldest example I know of is Temple of Apshai from 1979, and Dungeon Master (1987) was real-time and had stamina regeneration.

-May also include online cooperative play or PvP - I think this has existed since the game Habitat from 1986, at least PvP.

-Player vulnerability/immobility while healing? - I wasn't sure if this is really considered an important part of the definition but I've seen it in a couple of newer metroidvanias that are compared to souls-likes now. The first action game I know of that does this is the craptastic Sword of Sodan from 1988, though I doubt it's an influence on souls-likes. System Shock and Diablo 2 are similar in that health is restored gradually over time.

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Got any other examples? Also note that I'm not saying these exact games influenced Demon's Souls etc.

The devs (well, Miyazaki) themselves have had this to say:

"The Legend of ZeldaandDark Soulsare different games belonging to different genres though, and they’re guided by different concepts of game design. They don’t need to aspire to the same ideals. If there are similarities, they probably stem from the fact thatThe Legend of Zeldabecame a sort of textbook for 3D action games."

"The initial concept for Demon's Souls came from FromSoftware's King's Field series, with Miyazaki citing its dark tone and high difficulty as the main inspirations for the game."

"Miyazaki stated that the game draws direct inspiration from earlier works of fantasy and dark fantasy, especially the manga series Berserk."

From this video: https://www.youtube.com/watch?v=RpucyxeRxDI

Summary: hp lovecraft (king in yellow), conan movie (1980s), excalibur movie (1981), frank frazetta's art, fighting fantasy (sorcery), vinland sagas (norse history), lost kingdoms (2002 game)