We all have our moments of self-doubt, and I've never met or heard of a writer who doesn't get that creeping not-good-enough feeling occasionally (if not constantly) along with the rest of humanity. Reading an amazing novel can affect me in the same manner that viewing a Picasso might affect an aspiring artist, the way watching Kenneth Branagh play Hamlet might affect my actor son. When I read something incredible, yes, I worry that I'll never be able to measure up. The opposite of that concern is the hope that what I've written is worthy of comparison. That what I've written is maybe even good.
These self-judgments are just flip sides of the same coin, yeah? Neither is the complete truth, by itself. Put them together, and you get a realistic view of your abilities, as well as the motivation to continue creating. It's good to think what you do has value, but the fear that what you've done isn't good enough is also useful - it keeps you from settling for mediocre effort and striving to do the best you can do.