United Airlines is a typical American airliner. The online booking process is pretty smooth and you can reserve and make changes relatively easily. The selection of available flights could be better but the same could be said for most airlines.
Airport check-in has gotten better recently as they have installed self-service kiosks at most of their airports. Once you have boarded and are seated, again, pretty status quo. I haven't had food other than snacks in many years on a United flight so I won't comment on that. Drink selection is pretty varied which is nice and the cost is nice and low as well. Flight attendants are generally friendly and knowledgeable.
Baggage claim can be a nightmare but I think that is more the airport than the airline. Overall, pretty decent experience. Not much different than American or USAirways or any of the others.