I have been in the US for 18 months now and it is (supposedly) permanent as DH is American. We are in the North East so I can't speak for Arizona. However, I am finding it really hard at the moment. I really didn't realise how much I would miss my friends, and I don't seem to be able to get beyond surface friendships here. In the UK, you have a mutual "Britishness" with anyone new that you meet - there is some level of innate understanding. Here, that isn't there. I find myself withdrawing from people slightly for fear of saying the wrong thing etc. It depends on your personality - if you are outgoing and confident you probably wouldn't worry about this!
Lots of things are brilliant about here - we are near the sea, the weather is much better, service is great and I do love the general positivity/optimism of a lot of Americans (just wish it was rubbing off on me!).
Some things aren't so great - it is a properly capitalist society, you have to pay for everything, there is no national health care system (as you know) but also no child benefit, no help with preschool costs etc etc.
Will you be near friends/family? My DH's family are near us which has been a lifesaver. Can you go for an extended visit before you decide? Does your DH want to go? Can you agree with him that if either of you is really unhappy you will come back? Do you have children? One of mine took to the whole thing like a duck to water, the other one has had a hard time adjusting.
If you have any queries re the green card, let us know, it is quite a process in itself.
Riven is right, they are different to us!