Don't assume I disliked Narnia because it's a Christian allegory -- it isn't that simple. I disliked it because it made no sense. The lion sacrificed himself, and then pulled out a magic get-out-of-death-free card, and this was supposed to be good? A story with such a blatant deus ex machina just bores me, I'm afraid.
Which is a rather funny additional comment for a post showing preference for His Dark Materials over the Chronicles, given the layers upon layers of deus ex machina in the former.
In fact, it is highly unlikely that anyone is ever bored merely by deus ex machina, however blatant; it's hard, for instance, to get more blatant in this respect than Euripides, but anyone who claimed to be bored by Euripides's plots is merely showing that they have no taste in matters of drama, or else merely showing that they can repeat clichés without thinking about them. Deus ex machina is not intrinsically boring; so deus ex machina cannot, simply in itself, be the reason someone is bored.
I find it interesting that there is such common animus against deus ex machina as such, given that none of the standard complaints against it as a plot device can withstand serious scrutiny. None of the standard criticisms really apply to classic cases of deus ex machina like we find in the Medea or the Iliad or Brecht's The Threepenny Opera or (for that matter) Wells's War of the Worlds. The bias against it has a good pedigree, of course -- it goes back to Aristotle's Poetics:
As in the structure of the plot, so too in the portraiture of character, the poet should always aim either at the necessary or the probable. Thus a person of a given character should speak or act in a given way, by the rule either of necessity or of probability; just as this event should follow that by necessary or probable sequence. It is therefore evident that the unraveling of the plot, no less than the complication, must arise out of the plot itself, it must not be brought about by the deus ex machina - as in the Medea, or in the return of the Greeks in the Iliad.
Similar views are found elsewhere. Aristotle's judgment here is more limited than it might look at first glance; the rejection occurs within the context of tragedy, and, even if accepted for tragedy, is much, much less plausible for comedy. (Here's an interesting discussion of deus ex machina in Greek drama, and the differences between tragedy and comedy in this regard.) Needless to say, if you transfer to other genres than drama the matter becomes even more complicated. But even Aristotle pulled back from outright rejection even for tragedy:
The deus ex machina should be employed only for events external to the drama - for antecedent or subsequent events, which lie beyond the range of human knowledge, and which require to be reported or foretold; for to the gods we ascribe the power of seeing all things. Within the action there must be nothing irrational. If the irrational cannot be excluded, it should be outside the scope of the tragedy. Such is the irrational element the Oedipus of Sophocles.
Thus even in Aristotle the rejection of deus ex machina can be traced relatively precisely to particular requirements of one particular genre; a general ban can't be pulled from it. But even in Aristotle there is much to question here, as is shown in the criticism of Euripides and Homer; certainly Euripides uses deus ex machina in a way consonant with his overall (and high-quality) approach to tragedy: the gods jump in to resolve the matter but it makes sense at a higher level than the sequence of the plot. (And in the case of the Medea I would argue that Aristotle is clearly wrong in his diagnosis, since I would say the play shows that you can have both a god from the machine and a plot structured on plausibilities.)
The real issue, it seems to me, is not deus ex machina but quality of resolution, which has to be argued for based on the features of the work in question; there is no particular feature of plot structure that indicates poor resolution, but clumsy uses of deus ex machina are memorable, because unintentionally comical or jarring, examples of such poor resolution.