The Cheers bar does not look anything like the “set” on the TV show. It is a small bar in the basement. That is a total tourist trap. It does look the same from the outside.
I would suggest to anyone visiting Boston to go to the Warren Tavern in Charlestown. It has not changed much since the late 1700s. When Ben Franklin liked to hang out there when he came to town.
Another spot is the Union Oyster House. In the Fanial Hall area. It is very touristy, but has not changed all that much either in the last 200 years. You can sit at the raw bar on the same bar stool that Teddy used to like to get drunk at. Or you can go upstairs and sit in the booth that his older brother Jack used to like to eat.
There are also great Irish bars in the the Quincy Market area. Plus there are at least six bars outside of Fenway where beers are flowing: Game On, The House of Blues, Cask & Flagan, and the Bleacher Bar, etc.
Take in a game at Fenway. The team sucks but the park is still pretty cool to see. It is pretty similar to what it looked like when it opened in 1912. Thankfully, they added more bathrooms. But you will miss the “experience” of pissing into a Stainless Steel tough where the drunk guy from Southie next to you throws up and pisses on his/your shoes. People also no longer piss in the sinks. There are still posts with obscured view seats behind that 12” wide I beam. Also, out in the bleaches is the one RED seat where Ted hit his 510’ home run(and he wasn’t juicing).