1) The ARG as text can only be read through whatever the most-final version of the most prominent, collective fan theory exists, in a relatively concluded state.
This comes in a variety of forms: the archived/mostly dead message board, the mostly dead subreddit or reddit.com/r/ARG or 4chan's /x/ (or whatever) thread, or, most commonly at this point, the locked Google Docs file. Any attempt at reading an ARG should, of course, attempt as much of a playthrough as is possible/feasible. Using the playthrough as a basis of reading is not enough, however. What remains of the ARG is the combination of its viewable/playable artifacts and its active interpretive community over the course of its creation.
2) Any estimation of an ARG must read it through its capacity to engage with the paranoid reading.
With The Lost Experience ARG as the genre's only canonical example, the interpretive standards of the ARG community were set nearly a decade ago. This has had some consequences. Most obvious among these are that 'viral' marketing ARGs, like The Lost Experience or Halo 2's "I Love Bees" campaign, are aesthetically indistinguishable from non-marketing ARGs like the Jadusable/BEN DROWNED/Haunted Cartridge ARG. On a technical level this is fairly obvious: all forms use a mixture of the same tools, such as websites and accounts on established platforms like email or social media. Many use similar techniques as well, such as burying pertinent information in non-UI aspects of these accounts. This includes password-protection of pages that need to be derived from, say, accompanying video as well as parsing the page's code for clues. The more important aspect is that it has defined the shape of interpretive possibility.
Every, or nearly every, ARG that I have experienced (mostly second hand) has produced one of two (or, more often, both) interpretations, both of which I would classify under Sedgwick's idea of paranoid reading. These are:
a) Conspiratorial Interpretation: the ARG is best explained by reference to some set of conditions in the world -- usually assumed to be some sort of secondary world -- that are predicated on conspiracy. Whether explained through apocalyptic change, an abnormal acting of time (travel, split, &c), or the sudden empirical demonstration of the supernatural, these theories develop an interpretation of the gathered evidence that relies on some sort of potent, shadowy force (often something within the government or an especially shadowy, powerful private corporation) that is causing events to unfold as they are.
b) Psychological Interpretation: the ARG is best explained by reference to some (set of) psychological conditions experienced by the characters portrayed within it. These interpretations are -- in addition to being (near?) universally ableist as fuck -- premised on an understanding of the 'unreliable narrator' that still assumes the existence of objective information within the text. These are primarily non-secondary world theories, though not exclusively, and are often used to explain apparently supernatural or inexplicable behavior or phenomena through colloquial understandings of non-neurotypical experiences.
This mixture of history and technique have lead to these two being what I would consider the baseline of work for ARGs interpretive communities. Any reading of an ARG would therefore be required to explain not that these exist, but in what way they manifest or are explored beyond the most basic versions. A successful ARG might undermine these readings in exciting ways, or it might develop them perfectly.
This proposal, to be clear, is in the same spirit of suggesting that we might judge a novel by the believability of the motivations of its characters, or a film by the clarity of its story. There isn't an answer here, or a demand that things must be made in certain ways; it is obvious to me that this sort of proposal is immediately meant to be undermined. The difference, of course, is that ARGs don't have, as yet, any sort of explicit set of rules for reading, which means instead of breaking them they simply abide by those implicit.
3) ARGs should be read alongside creepypasta, fantheory/fanfiction, New Media projects, and alternative games as well as alongside marketing rhetoric.
Some crossover in these categories is already obvious; I Love Bees and The Lost Experience are explicitly creations of marketing departments, while Jadusable is an ARG that spawned out of one of the most popular creepypasta. Many ARGs make use of New Media/alternative games ideas and creators to develop their properties, and, if we allow for (1), any ARG is incomplete without the explicit involvement of something like fantheorists. The point in making this explicit is to say that not only do they share material linkages, but aesthetic techniques that can be explored by a reader.
In addition to sharing real, material labor (as in, people who have sold their labor time and expertise to (become the) creator of the piece in question), all of these forms are in some sense beholden to the labor of valorizing the internet as a medium. Creepypasta is already colloquially understood as "campfire stories for the internet," fantheories produce engaged affective communities around (mostly) corporate owned intellectual property on (mostly) corporate owned platforms, New Media is ideologically bound to the understanding that artistic practices are advanced using (mostly proprietary) technologies, alternative games are fundamentally tied to distribution platforms that develop through the internet. Marketing is the beating heart of the internet, from AdSense to Adblockers.
Those who want to read ARGs, either in this capacity, or as potential creators or simply as interested consumers, need to know at least a little bit about how the internet's campfire stories are constructed to teeter on the edge of realism, which is as reliant on platforms as on aesthetic techniques. They need to think also about how platforms and distribution models differ within the context of the internet, and about how production around intellectual property is navigated within fan spaces. And, of course, they need to think about how all of this is made, and funded; at least I think they do.