If you are limited on time in Boston I would skip Legal seafood's. It's just standard american seafood but there's plenty of other amazing places to go to. I love Union Oyster House though! What type of seafood do you like? If you like oysters Neptune Oyster is amazing but the line can get long in the summer. I would hit up Mike's pastry and Modern Pastry in the North end as well. The good thing about Boston is that it's very walkable. Spend some time in Harvard Yard/Cambridge as well. I spent 6.5 years there and the wife and I are going back this fall to visit our old spots. Let me know what kind of experience you are looking for and if you need sightseeing tips or itineraries!
Boston food places to go:
Toro- Spanish Tapas
Top of the hub- If you don't want to eat here you can hit up the bar for a great view of the city and Fenway from up top.
Pinnochios- Famous Sicilian hole-in-the-wall Pizza in Harvard Yard
Bartley's Burgers- Famous Burgers in Harvard Yard.
Burdicks- Cafe/Chocolatier/Bakery in Harvard Yard. Mrs. Gummi and Mark Zuckerberg's favorite.
Craigie on Main, sit at the bar for the burger. Make sure it's still available because they used to limit how many are made per night. It's the best burger I've ever had, hands down:
http://aht.seriouseats.com/archives/2012/01/video-the-craigie-on-main-burger-cambridge-boston-ma.htmlAnything[urlhttp://barbaralynch.com/] Barbara Lynch[/url], Sportello In For Italian, Butcher Shop for American/ smoked meat, Drink for cocktails, Menton or No.9 Park for $$$ Prix fixe.
Flour BakeryGah!