The syncretism levels are off the charts, and it's great fun so long as you get that McLuhan was no Einstein, in that the great physicist pretended, in knowing he was nearing the end of his life, neither to himself nor anyone else that he, though convinced of his own talents as he was, had finally discovered the Theory of Everything which would have served quite fittingly as capstone and farewell. Like Nietzsche, McLuhan had little compunction about inserting himself among the titans, obsolescing, at least in his own mind, reams of scholarship from all those inferior thinkers who failed to perceive the ground upon which they thought. But should we also grant him the title of Dynamite? Let's first assess the effects of his work.
If we go by academic popularity, Laws of Media was a non-starter (one might say it fizzled out) even among McLuhan's literary milieu. Did it fare any better with the public at large? Judging from the low number of ratings it has on this website, no, especially relative to the texts of Kuhn and Popper—both contemporaries, both worse publicists—who also had to push their memetic signals through in an ecology of declining literacy increasingly mediated by electronic noise. So we can safely say it had more bombast than blast.
What about the ideas themselves—do they hold water? I was glad to see, in the second sentence of the Introduction no less, the claim that "This essay offers in testable and falsifiable form (the criteria of scientific laws) observations about the structure and nature of things man makes and does," and later on, that "While empirical, [the tetrads of our science] provide a basis for prediction, for example, that retrievals or reversals of a certain form will occur." I was dismayed to see, in the remaining sections, no experiments proposed as to how a tetrad may be tested, no indication of what the criteria for a successful falsification might be, and no general or specific methods for properly determining predictive power. I do not think Popper and McLuhan would've agreed as to how the former's terms were to be construed. I think the latter took a fast-and-broad reading and asserted it multiple times with a confident tone—no substitute for qualification, so his thesis bears only the patina of science; holds no water on the terms it attributes to itself.
What about on other terms? Can the tetrad at least be incisive as a mode of conceptual analysis? Yes, I think, if we take for example "Hermeneutics" (page 140), which does enhance clarity, does retrieve depth, does reverse into obscurity when done to excess, and does bury naivete; each sense in which hermeneutics performs these actions is easily seen, that is, pattern-matched to prior experience (though this is insufficient to render its tetrad scientific; only descriptively resonant). If we take, however, "Booze" (144), which apparently enhances "private outlook, energy and zest, aggressiveness," we can add to our "Yes" a "but not necessarily." Nobody needs reminding that alcohol is more commonly categorized as a "depressant," or that only a select proportion of drinkers becomes more aggressive; and if by "private outlook" is meant "interiority of introspection," I suspect this mostly applies to a special tiny class of littérateur which does not drink to forget or to socialize.
Why the credit card should obsolesce "money" (as opposed to "paper cash") is a mystery to me, as is why Aristotelian Causality intensifies into Formal Cause in particular. How the car obsoletes the horse-and-buggy is apparent, but how "Crowd" obsoletes "the individual, private identity" is not. Specifically, though it may be true that one "loses oneself" while part of a crowd or mob, that crowds exist does not obsolesce private identity in anywhere close to the way that that cars exist obsolesces horses. And here obsolesce takes on two similar-but-orthogonal entendres, which is about as kosher as saying the written word and the telescope both "extend the eye" (117). Whether this is multimodal 4-D analysis or sloppy sense conflation I'll leave you to judge, but I at least felt like saying "That's a stretch" to many of the attributions made herein; anyone can take a concept, find the loosest interpretation still applicable as metaphor for another concept, and claim connection. So hermeneutics also intensifies into apophenia, you see.
A couple last notes. Firstly, the final sentence "Else we will have no more control of this technology and environment than we have of the wind and the tides" posits control as a sort of telos for the New Science and as a self-evident desideratum. Why should it be? I have my own answers, but a chance to compare and contrast would've been nice. Secondly, if we do decide to take his claim to place at face, McLuhan is still very, very obviously the third in a sequence of Bacon, Vico, McLuhan… Who is be the fourth grammarian? Whose tetrad shall complete the tetrad of tetrads?