I just wrote a bunch about Watertown
here. I think it's a really nice place to live, tons to eat, nothing really to do in the town itself besides a handful of pubs, a climbing gym, mall, and some nice bike trails, but it's so convenient to other places around Boston that it doesn't really matter. People are pretty civic-minded and involved in the community. It's like a cross between a small town and an outer neighborhood of Boston.
Commute downtown is about 15 min by car with light traffic, who knows during rush hour. If you live near the 71/73 bus on the east side you can be door to door to Park St. station (change to red line at Harvard) in 25-30 min in the morning or evening. Nights and weekends are slower because the buses don't run as frequently. West side or 70/70A to Central takes longer, probably more like 40-45. There are also lots of new bike lanes and some good bike paths.