I normally don't comment on bad service but this is my observation/opinion on United. I try very hard to fly other airlines. 

My impression is they have very unhappy employees. For that, it starts at the top.

 Majority are decidedly less than friendly and not helpful. Even with a handicapped passenger who could not physically put their carry-on in the overhead. The crew refused to help, said they could not. Finally a 2nd passenger stepped up and helped after watching the passenger struggle for a few minutes. I have not flown United for a little over a year so maybe this has changed but I kinda doubt it has.

On a positive note: my experience is they are wonderful to the animals they fly for rescues etc.