I fly to Europe and Asia at least once a year, and somewhere within North America at least once a year. I've flown both coach and business class on all of these.
Consistently, the US<->Asia flights are incomparably better. If I could pay a little more and get a Korean Air flight to Paris, I'd do it. Coach on various Asian airlines is about as good as some European and North American airline's business class. Seat comfort, level of service, aircraft cleanliness, etc.
I'll add that my back is ready to go out on even a D.C. to Denver leg on United, and I've almost never flown domestically and not gotten some kind of upper respiratory infection as a final parting gift. Air France, Lufthansa, KLM, British Air, United International to Europe is a similar experience, just longer and more horrible.
U.S. East Coast to Seoul nonstop is one of the longest routes in current commercial service, and I've hopped off the plane refreshed and ready to go do things every time. The standard kit in coach even includes an eyemask to help you sleep and the flight attendants bring around hot towels every so often so you can wipe down your hands and face. Bathrooms are well stocked with toothbrushes and toothpaste and getting water or snacks outside of regular meal time has never been a problem. On some flights they'll even give you cans of spray water to spritz on your face to cool off and refresh yourself. Food is consistently "decent". And paradoxically, seats are wider, better cushioned and more comfortable than the business class seats I've flown on to Europe on flights half as long.
I wish there was some way to bring this level of service to Western airlines, but to be honest, I count a domestic flight on United a success if all the lavatories are in service and don't overflow into the aisle.