Legal Seafoods is really nice and they're located all over the state. Two of them are located both at Copley and the connecting Prudential center so you won't have much difficulty but they aren't by the water. Other potential alternatives would be, if you like Italian food: Vinny Testa's off Beacon avenue in Brookline and Maggiano's in Boston's theater district, which is really nice.
There's a variety of places in the North End and some of them are exceptionally classy and the service is fantastic but only if you like Italian. Another really great place I can recommend, which is also located in Brookline and located off Beacon avenue is the Golden Temple, which is a semi-fancy Chinese restaurant and the prices are average, not too expensive and not too cheap but just in the middle.
If you're willing to travel, try the Cheesecake Factory which might be appropriate. There's one located at Cambridge's Cambridgeside Galleria and at the Atrium Mall in Chestnut Hill. They're not really semi-fancy if you're expecting to have eight forks for your meal, but they're a pretty classy restaurant, there's tons of variety on the menu for everyone, including children and the desserts are good. The prices are almost similar to Golden Temple.
For more info. on finding local restaurants, try this:
www.phantomgourmet.com
Phantom Gourmet is a locally produced show aired in the state that covers restaurants all over New England, and they identify virtually ANYTHING associated with food, and they've really got the 411 on what to find.