I think that's the context in which you should view these books. As literature... well, let's not go there. But they do make some interesting characters, they do keep the action moving, they do at least make an attempt (IMHO) to take prophetic Scripture seriously and envision how it might play out.
You have to ask what an artist set out to do. Chicago's 25 or 6 to 4 is terrible as an oratorio. But it isn't an oratorio, it's rock -- and as rock, it's one of the best. How is Normal Rockwell, as a classic painter? Or Stephen King as a Novelist (note the cap)? Or Jim Carrey, as a Shakespearean actor?
So I just don't approach the books that way, so I'm able to enjoy them... mostly. I could really wish (=do really wish) that they'd done WAY more homework on the character of ben Judah, since he's so central. (More on that available on request.) I find some plot developments lurchy and inadequately-handled (though some are, I'll confess, totally page-turningly involving). But I have read every one, and I enjoy them as a light, speculative read.
BTW, Peretti has confessed that his quality needs work, and says he's trying very hard to hone his crat. Anyone seen the fruit?
Dan