A lot of businesses who traded with the contininet now have trade barriers in place that mean they can't compete and sometimes can't get stuff through customs. Small companies have been crushed by this.
Brits can no longer freely move around the EU for work or study or just for a change. (I was looking at a soccer data analytics course at Upssala university recently and it is free to EU students but pricey for others).
We've lost an incredible number of highly qualified tradespeople and professionals who are no longer free to live here.
We've had to negotiate trade deals with other countries that we'd had an automatic deal in place with as part of a huge trading bloc. Now we are at a massive relative disadvantage. By all acounts we're being shafted.
We're a laughing stock.
None of the claimed benefits appear to have materialised.
It's sometimes hard to fathom for me, at least as an outsider looking from across the pond. From what I've heard from various Europeans (not just here on RF), the EU seems to have mixed reviews. Some think it's wonderful, and others, not so much.
Around the same time as the formation of the EU, there were those in North America pushing NAFTA and envisioning a continental/regional economy patterned after the EU, even proposing a common currency, the Amero. There were those who even envisioned AFTA, a unified open trading bloc encompassing the Americas and the entire Western Hemisphere. I actually thought this idea had some promise, but only if it were a democratic-socialist economic structure - which the Powers That Be would never go for.
But in America, as well as in many other countries, there seems to be an underlying resistance to the idea of a "global economy" or any kind of unified "world government," regardless of what form it might take. I myself have mixed views on this, although I have to concede that ultimately, humanity's only hope for survival is to eventually unify in some form or another. I'm just not sure how that would be done or what form it should take.