Bukowski's Tavern is supposed to have a good range of beer. It's on Dalton St, down the end of Boylston, so I think that is the Back Bay area? Make sure to take your passport if going, as they won't accept an Irish drivers licence in this place, no matter how old you look! I didn't get in after long converstation with burly doorman, so don't blame me, if it's crap!
McGreavies is around the corner from that, and doesn't have craft beer, but has a lively atmosphere! If in there, try the pickle backs, which is a shot of jameson followed by a shot of pickle juice, or maybe don't, as probably not the most sensible thing to do.
Depends what you are into, but practically every Bar in Boston has Harpoon IPA as a minimum decent beer, and if it doesn't, I would get out of there, and try somewhere else.
All in all, Boston is a great drinking city in my opinion, so enjoy.