Much of the leaf drop is probably due to an insect called the maple petiole borer.  This is a small wasp-like insect as an adult; it lays eggs into the petioles of developing leaves in the spring.  A tiny grub stage feeds inside the petiole for a few weeks.  The leaf petioles often break at the feeding site, resulting in fallen leaves.  This is usually only a spring-early summer insect, so leaves falling later in the year are likely due to something else.  Second photo-- the small upward projections on the leaves are galls cause by the maple spindle gall mite.  These look odd, but there is no true harm to the trees.  Third photo-- middle leaf has a broken petiole, so the petiole borer caused this one to fall.  The other two fell with the entire petiole attached, so it was from some other cause.  Wind, heat, drought conditions, many more things could be involved.  Maples can tolerate losing many leaves without any issues, so I do think the tree is in any sort of trouble.