I've had the pleasure of sitting in 340 only once, for a Raiders game last season. The Pack won big and the Packers fans treated it like a playoff victory. The corner angle isn't a bad seat at all no matter which of the 12 rows you end up purchasing your tickets for. The only thing I would suggest is purchasing one of those comfortable stadium seats to take to games because those bleachers will make you sore after 4 quarters.

The Packers organization realize that the it's not the size of the venue, it's the people that fill it. There literally isn't a bad seat at Lambeau Field, as you can still get a great view of the action even from the top row of the top section.
The Packers fans are fantastic. You feel like you're sitting around a bunch of your friends' friends. People you just met, but feel ok around. The tailgating is great as well. Whenever you walk by tailgators, people will offer burgers, brats, beer, shots, whatever they think you need.