Boston's a great city. It has a lot of history and you can see a lot just by walking around. Boston common is picturesque too. Transport around the city is pretty good too, though most places are pretty easy to walk to within the downtown area. Cambridge area and Harvard University are well worth a visit too.
Insider Tip:Club Passim just off Harvard Square is excellent. Was there for the campfire festival on memorial day and there was some excellent music. The club has bands on mostly every night and also has an adjoining vegetarian restaurant, Veggie Planet, that serves excellent food.