Welcome to the club.  The closer I get to the end of a project (short or book-length, fiction or non-fiction or poetry), the more I suspect I have failed.  Why?  Because the power it had to grab me has dissipated, and it seems to contain nothing but a pile of dead adjectives.  The next time this happens to you, remember this:  When you’re halfway through a piece, half the surprise of it is gone for you.  Near the end, there’s almost no surprise left.  You’ve burned it all up in the process of creation.  But for your reader, the surprise, the hunger for what’s coming next, only builds.  So the sense of failure you increasingly feel is an inevitable part of the process.

I have learned instead to check off the elements that make up a piece.  For stories, fiction and nonfiction both: the keenness of dialog that a reader can hear, the description that creates a place where the story happens, and the behavior that reveals who people are and (even) what’s going on in their heads.  For expository writing, the junction points at which ideas merge, depart, are transformed.  For poetry, compression.  And if everything checks out, I tell myself, Therefore it has to be good.