What are the possible candidates for the most fundamental principle of reality, which is to explain everything else? Well, what do we know about the reality which it is supposed to explain? One thing we know from the study of Physics, is that the world can be described (at least most of the time, to a high degree of precision) by a mathematical system of equations.
So the world is made of math! (However, we should bear in mind here Bertrand Russell's observation that the fact that the constituents of the world are ordered in a particular pattern does not actually tell us what is the internal nature of those constituent parts...this will come back to bite us later.) Here I am speaking loosely, in the same rough sense that I said earlier that things happen due to magic.
Well, what should we conclude from the mathematical nature of physics? I can think of two obvious hypotheses. Either (1) the fundamental reality is something a bit like an mathematical equation (yet not a mere abstraction, but something which actually makes the world go around), or (2) the fundamental reality is something a bit like a mathematician, i.e. a mind capable of appreciating mathematical relations. (I don't mean either of these descriptions to be taken too literally here, obviously the fundamental entity cannot be exactly like a set of symbols on the blackboard, or a human mind, but the choice of analogy makes the difference to what effects seem likely to follow.)
If the former hypothesis is true, we would have Naturalism, a worldview which takes the universe as revealed by the Natural Sciences to be the ultimate reality, so that everything else must depend on that. If the latter is true, we would have a Supernatural or Theistic view of reality.
I don't mean to suggest that (1) and (2) are the only possible candidates for the fundamental entity, just the ones I find most plausible. Some naturalists might instead propose that the ultimate thing that explains everything else is A) the entire Universe “taken as a whole”, B) the first moment of time, C) the most elementary constituents of matter (whatever they are), or D) some vague principle or force, not structured like an equation, “out of which” the Laws of Physics emerge for some unknown reason. But I don't think these are quite as plausible as compared to (1).
I only have time to do a drive-by shooting of these proposals: (A) seems problematic as the unexplained source of everything, if we take the term “Universe” literally. For the Universe (as defined by Naturalists) is just the collection of all the things which exist (e.g. my cat). So if we say that the Universe as a whole just exists and has no explanation, that would imply that my cat, being one of the parts of the Universe, just exists and has no explanation. We could try to clarify this hypothesis by saying that actually only certain necessary, eternal, basic features of the Universe that have no explanation. But then it is no longer the world taken as a whole which is fundamental, but only some aspect thereof. We are then obliged to give a more specific account of what we mean by that aspect, and this is tantamount to adopting one of the other hypotheses.
If we say (B)—which obviously only works if there is a first moment of time—it seems problematic that the fundamental nature of reality should pass out of existence, and odder still why it should result in consistent laws of physics at later moments of time. (C) means that there are rather a lot of fundamental realities, and raises difficult questions about what makes them capable of interacting with each other, and how they can be limited to particular places or times. Without more details (D) is too vague to really be criticized, but in any case it is starting to verge on a (rather murky) Supernaturalism.
Now let's do a survey of Supernaturalistic views, in which there's one or more divinities, conceived as capable of having some degree of understanding, power, and purpose, although it or they might not be very much like a human mind. One could accept Pantheism and identify God with the Universe. Or one could embrace Polytheism and believe in multiple gods who are collectively responsible for the Universe as we know it. Finally, one could invest all of the responsibility in a single Deity who is the source of everything else, which is Monotheism.
Pantheism seems to be open to much the same types of objections as (A) above. (Many forms of Pantheism say that the universe of our senses is an illusion and all that really exists is God, but I have difficulties making logical sense of this position, so I won't consider it seriously.) Also it is not entirely clear, if God is identified with the Universe, how this viewpoint can distinguish itself from Naturalism, although some Pantheists might have answers to this question.
Polytheism seems to me susceptible to fatal objections, at least if the gods are regarded as metaphysically fundamental. It seems rather strange that a bunch of fundamental entities should coexist without there being any higher principle which determines why the Pantheon is related to each other in the way that they are. What decides which god gets its way in the case of a disagreement? (Or if they always agree, that would seem to suggest something deeper than any of them which causes them to agree.)
Indeed the actual historical Pagans, despite worshiping multiple gods, very seldom conceived of the vast panoply of gods as being fundamental aspects of reality. Instead they usually invented elaborate theogenies explaining how the gods themselves came into being (by a variety of scandalous sexual or asexual means of reproduction) from pre-existing matter or divinities. Often one has a henotheistic setup: worshipping one chief God who is regarded as the primary Creator, together with many lesser gods valued as mediators to the heavenly court. Or else the different deities are regarded as modes or manifestations of a single one. Thus, even in polytheistic cultures, the philosophers tend towards Naturalism, Pantheism, or Monotheism in their fundamental philosophy. This is a tell-tale sign that a religious belief is philosophically untenable: if even the philosophers raised in a tradition cannot accept it.
Notwithstanding the platypus, it seems rather unlikely that Nature was designed by committee. It has too much internal coherence for that. Atheists are frequently heard saying that Modern Science is in conflict with Religion, and they are quite right, always assuming that by “Religion” they mean Paganism. It is quite untenable in a Scientific Age to believe that there is one divinity responsible for lightning, another one responsible for erotic love, another for birds and so on. The natural world isn't really divided along those lines.
As far as I know there are no polytheists who worship the actual forces of nature as four different gods. The best I can do along these lines is to suggest that Thor = electromagnetism (obviously!), Odin = gravitation (he's the most subtle), Freyja = strong force (she who binds with ties of love), and Loki = weak force (too busy wreaking mischief to bother holding anything together). But I think this new cult is unlikely to take off among any demographic group I can think of!