I have flown UAL ORD-HKG 4 times, and was very disappointed each time.
On this 16-hour flight, which is the longest in the world, only 2 meals were served ( doesn't taste good of course), plus a "snack box" ( same EVERY flight: 1 chiken flavour instant noodle, 1piece of cheddar cheese, a few pieces of crackers, 1 almond cookie, 1 tiny serving of fruit).
Service was extremely bad with rude flight attendents who 'scolds' people.(really, the female F/A scold and old lady because the lady didn't speak english and ordered the wrong food).
I strongly recommend you NOT to fly United Airlines.