In flight service down the back nothing special, no significant difference between any other transatlantic carrier. Some days it's better than XX, sometimes worse. Have mixture of US and UK flight attendants so will get unpredictable cultural differences in service. Booze is free.
Where United are slightly better that the competion is their Economy Plus section which has maybe 8-10 rows over the wing section of the economy cabin. If you don't have 'status' you might get lucky and be put in those seats when you check in, they have an extra 6" approx of leg room and are good compared to the seats behind. Depends on the load really, the fuller the plane the better chance you have. If it's empty they will block seats out for their frequent fliers to have an empty seat next to them.
Ugrade to bus class without status is pretty unlikely, UA use their business cabin to reward their frequent fliers and without an upgrade certificate or status you will have a lot of others in front of you. Might get lucky of course, op-upgrades can come out of the blue for non-status pax, even on BA!
