I went a couple weeks ago and watched them lose to the cowboys (I live in Wisconsin).
The fans were decent to the cowboy's fans. The food in the stadium is extremely expensive, and you will want to dress warm. The seats closest to the field are bench style, and the higher up seats are actual seats. Overall it is a good experience. If you go early enough there is a gas station by a chain of businesses that sells parking for 30.00 and its not to much of a walk from there, otherwise you will be hard pressed to find parking at the stadium itself. I also found it easier to avoid the traffic parking down near the parking near the gas station.
I just went for the first time last week for the Bears TNF game. People were generally nice enough. The entire stadium will do the "That's another Packers.... FIRST DOWN!" thing every. single. time. Aside from that, it's awesome to go there. There's a brewery right outside the stadium called Badger City I believe and they had a big selection and the Red Ale I got was good. Gotta get some cheese curds while you're there. Stadium is cool, fans are passionate, and food is good. I had a great time, lol.