I was able to make a stop at both of the major breweries in Boston in one day and will have to say Harpoon was my favorite. The staff is amazingly nice and do a great job of taking you through a fully operational brewery. The bar is great with long German beer hall style tables to meet new people and take in a great view of the city! Also when speaking about the view I must make a note to the guys to be sure to use the restroom as the urinals also have a great view of the city.
Also, I highly recommend getting one of their spent grain pretzels. Almost as good as the beer!