Brit living in the US here.
In my experience, Americans are only superficially friendlier, and it tends to be restricted to a specific situation. For example, I used to regularly attend a gym class, and chat to the same few people each week. After about six months, I suggested that we go and get a coffee together after the class. You’d have thought I’d suggested a mass orgy in the swimming pool by their reactions. Also, if you’re invited to an event, eg a BBQ, between 12 and 2, then it very definitely starts at 12 and ends at 2 - no lingering for a relaxed afternoon chatting with friends.
As others have said, a lot of Americans are big into God and guns and have no discomfort in reconciling the two. It’s noticeable round here that religion and large families are very common, and it’s not unusual to see a young woman in her mid-20s with 4 kids and pregnant with a fifth.
They are obsessed with the military, to the detriment of everyone else. I live in an area with a large military population, who are frequently worshipped (I was once chastised for not allowing a serviceman in uniform to cut in front of me at the supermarket - I hadn’t even seen him!), but extra taxes to support schools, firefighters etc are seen as BAD. Likewise, there is an obsession with sports to the detriment of academics. I think this is connected with the need to get scholarships for college/university.
They do drink less than Brits, but are way more likely to drink and drive. The standards of driving are generally pretty bad.
In the area where I live, there’s not a lot of stylish dressing or home decor.
Our experience of healthcare has been excellent, but the costs are horrific.
It’s a mixed bag really. I have met some nice people, but I do think it’s very hard to make actual friends here compared to the UK.