I actually had a rather pleasant experience here. That may be because I only returned my rental car here. I rented it from LAX (Los Angeles International Airport) and we drove out to Vegas after our California Adventure. So this review is strictly for car return.
Alamo Rent A Car is located in the McCarran Rent-a-Car Center. All of the car rental companies are located here. We pulled in and signs are clearly marked for each company as you make your way up the ramp and around the bend. I think Alamo was either the 3rd or 4th company. You pull in and they have you pull up to within 2 feet of the car in front of you. An associate came over quickly, checked our mileage, made sure we returned it with a full tank of gas and did a quick inspection. She then handed me my receipt and we were good to go. You then make your way into the lobby and exit the front of the building where shuttle buses are waiting to take you to your terminal at McCarran. The bus was waiting when we got there and left shortly after we boarded. Overall a good experience.