Brian Weatherson proposes a heterodox interpretation of the argument of the first meditation. At least, he thinks it is heterodox, and it sounds heterodox to me, but I can't claim to be familiar with the full range of Descartes scholarship. The interpretation also strikes me as having some merit; it does stand out, as Brian says, that Descartes never really solves the evil genius problem.
I've been teaching Descartes again, which has me pondering my own heterodoxies. Or at least, again, that's what I take them to be. In particular, I've been pondering the question of what this God that Descartes claims to be able to prove the existence of is. Some interpretive problems are solved (and others are generated) if for Descartes God just is the mathematical structure of the world, the union of all the logical and mathematical truths.
Of course, speaking of the union of logical and mathematical truths suggests a composite God, and the possibility of somebody being right about some parts and not about others. But all the parts are necessary, and anyway it's not clear that we should speak of parts in this case; all necessary truths are equivalent, after all, and necessarily so. On some ways of counting and individuating (perhaps the metaphysically appropriate ways), there is only the one necessary truth.
If that's God, then in attributing necessary existence to God Descartes is not saying much more than that the necessary truth is necessary, so it becomes less mysterious why he thinks this is something easily established by logic. Admittedly, there may be a tiny bit more; in talking about "existence," he may be implying a Platonism which would not necessarily be shared by everyone who thinks that there's a necessary truth which is genuinely necessary, but Descartes of course was a Platonist, and made a point of emphasizing that at the start of his 5th meditation proof for the existence of God.
Now, there are those who would deny this necessary truth; Mill, Nietzsche, and Quine would presumably all reject it, and many others would say that misleading things have already been said about necessary truth even in my highly abstract discussion. But while this wouldn't produce smooth sailing for Descartes, it would make his attempt at an ontological argument far less absurd.
The most glaring problem for this interpretation is that even if there is a necessary truth, it hardly seems that this would have the traditional attributes of God. In what sense is necessary truth loving or benevolent? In what sense is necessary truth a cause of the world? What sense does it make to worship or pray to necessary truth? What connection does it have to the Catholic tradition Descartes claimed not to be completely abandoning?
Perhaps most pointedly for Descartes specific project in the meditations, what sense does it make to say that necessary truth is not a deceiver, or if it can't deceive (perhaps because it's true, though it seems truth can mislead, or perhaps because it can't cause anything and so can't cause deception), how does the mere fact that there is necessary truth establish that clear and distinct perceptions must be infallible?
On the present picture, Descartes claim that God is not a deceiver is perhaps on a par with Einstein's claim that God does not play dice; an assertion that the ultimate principles of nature are not utterly cut off from us. This, of course, increases my suspicion that I'm being anachronistic in attributing this to Descartes, though perhaps it is not shocking that two great physicists might end up agreeing on some metaphysical points. But if that is what he means, I'm not sure what reason he can be seen as giving for thinking that it's true.
Maybe the unity is supposed to help here, though. If there's only the one necessary truth ultimately, then perhaps the notion is that if we can grasp it at all, and we seem to know a bit of mathematics, that means that the necessary truth is within reach (of course, if it's just one thing, it's puzzling how it seems we can know some necessary truths and not others, but everybody has that problem). Perhaps this is why Descartes makes so much of the fact that he claims to have an idea of God.
Of course, to be thoroughly anachronistic, most people these days think Einstein was wrong about the dice.