So, this is far more about American Airlines than about McCarran Airport. McCarran Airport was actually lovely. It is American that is a waste of time and money.
The service we received was horrible. The flight attendants were curt and insensitve as well as lazy if you were not located in first class.
The carry on luggage issue was ridiculous. Traveling from NYC our bags were perfectly fine to be placed in the overhead but, magically by the time we, all four of us, began to travel back to NYC from LAs Vegas our bags must have grown so much that we had to check our bags.
The seats were so close togerther that sardines felt bad for us and the poor treatment (they seemed to have been showered with some sort of greasy substance) that our forcibly checked bags received all added up in me NEVER flying American again, even if it were free.