Hey GreenEyed, I can't really compare as I have always lived in Germany, but here are some thoughts that might help you.
It's not that germans see their language as important but we think/know that it's a very complicated language, even for us

, so nobody will blame you for not speaking any german. A lot of younger people (younger than 35 years) will be able to talk to you in english, the whole group won't necessary switch to english completely as long as you are around, but that might happen.
I think people will react positive to you most time.
Maybe you get some information about us by knowing what rumors exist here about USA:
It is said that people in USA are not very well educated (sorry guys ;D) when it comes to anything outside america. So it might be a good idea to be able to find europe on a worldmap and avoid the question "Is Hitler still in charge?" and don't say: "Oh, you really got refrigerators in Europe?".
On the other hand we know americans as communicative guys who connect fast to each other, I think it might be true that we are more reserved in general. So you might have to show some initiative to find people to hang around with.
The german metal subculture is very open minded, I think your main problem there will be to handle all the beer you get for free.
Here are some some classic fun german topics:
Beer. We love our beer. There are three very different types of beer and the question which one is the best is a great topic. Just last weekend I put the line: "Oh, you prefer to drink 'Altbier'? Too bad, I was SO sure that you are cool." (worked great). [btw., "Altbier" is "Old beer" in english and descripe the taste perfectly.] You can start a conversation (in mixed sets, for example) with that topic, if you want to.
Angela Merkel. Our federal chancellor. It's very common to make jokes about her being ugly. So something like "I am shocked, I thought you all look like Angela Merkel" might work very well.
I personally like: "I think in germany you drink so much beer because you voted Angela Merkel as your chancellor."
I hope this is helpful for you. I wish you a lot of fun and girls in germany.