One the one hand, Maine maple syrup doesn't differ much from the maple syrup of other states, because it can be used in lots of recipes and always tastes great. But maple syrup is an old Maine tradition—even to the point of having a law that defines how Maine maple syrup is different!
The only state that produces more maple syrup than Maine is Vermont. Over 300,000 gallons of maple syrup came out of Maine in 2006. To give you some idea of how much work goes into that, it takes 43 gallons of sap to produce one gallon of maple syrup.
Like a fine wine or cheese named after its region, Maine maple syrup has to meet certain standards. According to state law, it can only be grade-A maple syrup, which means simply that it is lighter in color and texture than grade-B maple syrup, and is harvested earlier in the year. Unlike even other distinctly regional foods ("New England clam chowder"), Maine maple syrup actually has to be produced in Maine.
Contrary to popular belief, not all maple syrup comes from small shacks tucked away in the woods. Although there certainly are plenty of these in Maine, the northern part of the state has a good deal of larger farms with miles of tubing that the sap travels through. Syrup can travel for miles before it is even bottled!
There is even a day dedicated to Maine maple syrup. It's called Maine Maple Sunday, and on the fourth March of every year, maple sugar farmers open their sugar houses for free tours and tastes of the maple syrup. They show everyone the details of turning sap into delicious maple syrup and equally delicious Maine maple sugar candy.