The first thing to say is that America is so huge that your experience would vary enormously depending where you went - the big coastal cities like NY, Boston, LA are totally different from middle America or the South.
Good things:
General positivity, optimism and friendliness (latter more prevalent outside the big coastal cities), and a culture that celebrates effort and success. The UK seemed a really gloomy, bitter and envious place in contrast.
Huge opportunities for travel within the country - it has mountains, beaches, desert, swamps, forests, you never run out of things to visit, and petrol is very very cheap.
Spacious housing (most places). Outside the v expensive cities (NY, SF), you can rent a very roomy house with a garden and maybe even access to a pool for fraction of the price of a one bed London flat. There’s just more space to build.
Possibly good/bad things depending on your POV/circs:
Healthcare is excellent if you have good insurance. I will never forget my GP in the US - the first time I saw him he actually gave me a business card and told me to call him anytime. They were incredibly thorough, thoughtful and professional and had great health outcomes - for me the experience was 100X better than my experiences with the NHS. BUT - it’s true - if you don’t have insurance you are totally screwed.
Religion - if you are squeamish about God then much of America is not for you. There is a lot of God - you will definitely be expected to hold hands with strangers at Thanksgiving dinners and thank God for your blessings.
Bad things
Processed food. Supermarkets are FULL of coloured cheese, and sponge cakes with radioactive looking icing, and “whipped topping” that looks like cream but is in fact made of polymer and corn syrup. If you want to cook from scratch in a vaguely European way and/or don’t want to worry about the chemicals you are consuming you need to live near a farmers market, with a Whole Foods as back up.
Racism/legacy of segregation. Every country has issues with racism and discriminatory treatment of minorities, but it seems on a different scale in the US. In some places it feels like desegregation never happened. There are some really shocking inequalities and attitudes, even now. It is a huge issue which I think overshadows American society.