Although 340 is in the upper level corner, the view isn't all that bad at all. Following the football is fairly easy and I can still make out the jersey numbers but you can't read the names on the back of the jerseys. You will need decent eye sight to do that.

You can see all of the action in the North end zone with perfection. But of course, the closer the football gets to the south end zone, the more the view weakens. These are great seats and the only downside to your day is going to be the traffic situation both before and after the game.
Even though the stadium is located off of route 1, it's almost one in and one out. No joke, it could take you two hours after a game to exit the parking lot. The best thing to do is to go eat after the game at Bar Louie or the Olive Garden at Patriot Place and wait for the cars to clear out.