Fair question. I honestly can't put my finger on big things. For me it's lots of little things that probably seem trivial and stupid to others, but mattered to me. I was based in the mid West, but my experience may have Been very different if I had lived on the west coast. I do regret not giving that a try. I'd say to people just try it. You'll probably love it. Just go in with your eye's open. It's a great industry over there and the best thing is, no oztranaughts. You Will have experienced real weather, real terrain, cold weather ops, real ATC at the busiest and most complex airports in the world with (mostly) great crews.
If you come back, you will find it hard not to laugh when your colleague briefs you that the BKN008 in Sydney this morning is "a threat."
But I didn't like everything. Some things that come to mind;
1. The amount of degenerates and sketchy individuals everywhere. You always feel on guard and never safe. Even in nice areas.
2. The quality of fresh food is awful unless you pay a fortune for it. Everything is packed full of preservatives or fructose corn syrup. Bread is disgusting and don't even mention the coffee.
3. My wife and I were thinking of kid's and I'd never ever want my child to go to an American School. Even if they don't get shot, the level of education appeared a little... lacking. (Yes I am aware Australia is becoming more more dumbed down too).
4. Culture of working comes first, and taking sick days, mental health days etc is so frowned upon. (Look at some of the flow through agreements).
5. Lots Of things (outside of aviation) are very backwards.
6. Healthcare.
7. Many personal things I missed such as Sport etc which has nothing to do with the US and everything to do with me.
But, all of that is personal opinion and potentially meaningless to anybody else. I've lived In the UK, spent large amount of time in Asia etc and loved it, but I found the US the hardest to live in.
Some pretty balanced stuff there.