I bought my impala with 40,000 mile on it and I have not had much trouble out of it. I have had the water pump go bad, that has been replaced under extended warrenty. However, the tire sensor is broken and the temperature sensor is broken as well. My husband is 6'5" and he fits comfortably in the car with me. We have been in an accident where some one hit us in the back with a Ford F150 and it did more damage to him than to us. It it a safe car. My next vehicle will not be a car but if it was I would get another used impala. (no point in getting a new car, they depreciate so quickly). If dealers stand behind their product a slightly used car is just as good if not better (lower payments).
Stereo system, smoothness of the ride, acceleration abilities
Space in the back seat (im 5'9" and there still isn't enough space for others), tire and temperature sensors, also starter is acting a little funny. Key pad (have to be right up on the car to use it)