I've relied on the MBTA for years in the City of Boston, then when we moved to NH we still relied on it even more, it's been fairly consistant through the years. I never had any major complaints with it. The commuter rail is what you take the further out of Boston you go, for instance, living on the seacoast we're able to take it in either Exeter, NH or Newburyport, MA. I always used to take the train in Newburyport when I worked in downtown Boston in the last several years. The beauty of it is that you're not racking up the miles on your car, that's the most important thing in my estimation. You're not spending it on just gas alone all the time and also car maintenance constantly. It's ideal as long as you don't mind the train ride, you can finish so many books either manually or on tape, you just sit back and relax on the way in to North Station or on the way home.
There's also C&J Trailways from either Portsmouth, Dover, NH or Newburyport, MA as another way to get in to the Haymarket or South Station area of town.
The downside of taking the "T" commuter rail in is that in the winter months? Some times when it was absolutely freezing out? The tracks would freeze up and they'd be delays OR a few times we had some of the cars wouldn't have heat in them. SO you have to make sure to bundle up, because you freeze your toes off from what I could remember of those "few" incidences! They weren't all the time, mind you, but keep it in your head that it COULD happen a few times to you over a winter season and it's probably not going to stop happening with the commuter rail unless we (all of a sudden!) get Florida weather during the New England winter months!
It's still well worth it in the long run, you can go to the site mbta dot com and click on commuter rail and you'll see the fare and schedules for it right on their site.