Last night I laid in bed, debilitated by a bad piece of sushi, I watched Everyone Says I Love You, Woody Allen's musical comedy. I began to think about why some people love and others hate Woody Allen and his movies. I tend to hear "you've seen one you've seen 'em all" a lot. So I questioned why I fell in the love category.
Although almost all of his movies have the same basic plot, quirky writer/detective/schlub/whatever in search of true love, most have very different settings and genres. It's obvious that love is a common theme in most movies, but Allen takes it one step further by having one basic plot. So it is his ability to transplant this story into different settings and still have it work (arguably). Annie Hall is the classic and most basic version of this story, but then you put the story in a film noir, murder mystery, sci-fi parody or a musical. This exercise shows that the essential human emotions are what draw us to a good story.
I'd also like to point out that he does have a number of films that don't follow his usual style, and a few are pretty amazing. My two favorites from that group are What's Up Tiger Lily? and The Purple Rose of Cairo.