Well, bear in mind for starters that Waugh himself harbored retrospective doubts about Brideshead. Among other things, he thought the prose was overripe–a result, he claimed, of wartime deprivation–and did a good deal of paring and trimming when he prepared a revised version in 1960 for the uniform edition of his novels. The edition of Brideshead available in this country does not reflect these later changes, with which most American readers are unfamiliar. (For more information about them, go here.)
I myself find Brideshead flawed but rereadable. It has wonderful things in it, the comic scenes above all, but I do think it suffers as a work of art from the explicitness with which Waugh makes his religious points (as opposed, say, to Black Mischief or A Handful of Dust, where all is done by stealth). He did more or less the same thing far more effectively in the Sword of Honour trilogy–which, like Brideshead, is best read in the revised one-volume version prepared by Waugh for the uniform edition.
One of these days I’ll write an essay about all this….