I'm Scottish, but lived in California (San Rafael/San Francisco) for a few years. There were several things that astounded me about the U.S.:
You can't walk anywhere. We tried several times to walk to the mall, about 5 minutes away and found that the sidewalk ended abruptly at a main road; we also had neighbours constantly stop and ask if we wanted a ride. It was a 5 minute walk!
Portion sizes were HUGE and food was cheap. And very sweet.
Cashiers were genuinely friendly. In Glasgow you barely get eye contact and a grunt!
Americans are friendly but cool. Superficially they are very approachable, helpful, friendly but not friends...don't really know how to put it. Most people I met were extremely family/partner oriented - nothing wrong with that - but they didn't seem to have close friends, unless they knew them from childhood/school.
It was frowned upon to drink alcohol. Hey, I'm Scottish! Seriously, when I mentioned drinking wine at home or going to the pub at lunchtime it was recommended I join the AA....
The States is vast, largely empty and very beautiful.
Quite a few people I spoke to had no knowledge or interest in other countries.
Kids I met were all absolutely confident in their ability to do anything they wanted. Not arrogant (maybe entitled?), just extremely confident, and seemed confused when I asked what would happen if they couldn't be the next Britney Spears or George Bush, as though it never crossed their minds that not everyone gets to do what they want.
Guns and God were spoken about with fervour, which made me a tad uncomfortable. I've never seen anyone with a gun here in the U.K. and religious beliefs are not discussed usually.
I found it weird that medicines were advertised as better than similar alternatives, as though anyone without a medical background would be able to make an informed decision about self medicating. And the whole paying for health care - and the extortionate prices involved - baffled me. The NHS in the U.K. (and even better, Scotland, where we have free prescriptions as well as free health care (covered by our taxes)) is a wonderful thing in my opinion.
Overall my experiences in the U.S. were amazing and it's a wonderful country, but definitely different to Europe :)