Growing up on Nantucket, I rarely watched the 4th of July fireworks because all of the good spots would be filled with tourists. Since moving up to Boston, I've watched them from the Cambridge side of the Charles River, near MIT. You're right under the fireworks and it's an incredible sight. The Cambridge side is also much less crowded than the Esplanade and more easily accessible. Surprisingly, though there are more people in the city, the wide open space makes it significanly less overwhelming than watching on an Island.
This year, however, I decided to watch them from elsewhere. After a busy holiday homestand at the park, I didn't really want to be around mass crowds of people. The view from Mission Hill was a much different view than I was used to, but I didn't mind it. I had to stand on a chair outside on the balcony while trying to keep balanced (because as most people know, I'm quite clumsy) but the church in front of the fireworks was the icing on the cake. It made for some pretty spectacular photos.