Or you may not have this experience at all. The weather is not nearly as bad as claimed. The healthcare has its issues, but not having to divest your life savings for an unexpected trip to the hospital is a good thing. Standard of living can be very high. You will have a huge public transport network, bike friendly cities, some of the best culinary spots in the world, plenty of nature and green spaces, social activities, endless arts & culture, free museums in the capital.
Source: an expat living permanently in the UK.
Meanwhile America is being driven into the ground by Trump and Elon.
I have many expat friends living in London, which honestly is part of the motivation to move, and what you're describing is my expectation. Likewise agree that I don't think others commenting on this thread fully grasp what a uncontrolled disassembly the US is going through right now. Completely unprecedented.
Ad an expat/immigrant, I'll tell you my personal working definition, based only on my experience:
An immigrant is one who moves from a poorer country to a richer country. An expat is one who mixes from a richer country to a poorer country.
One cool feature of my definition is that it explains a lot of the cultural subtleties in comparing these groups: how immigrants adopt the local ways much more than expats do (expats retain that touch of superiority) etc etc
On average, every situation is different, this is just my general rule of thumb pattern I've observed.
It's a bit of a different thing. Expat implies working there for a few years before going home, immigrant implies moved permanently. Most Americans in London are the first one.