Service varies by the dealership. First, if the mechanics are not up to the task, service will be poor. This is a major issue when the dealer doesn't take care of its people and they jump ship when they gain experience. The more inexperience, the more "try this" and then "try that" as parts are replaced instead of proper diagnosis of the problem. Parts replacers run up huge bills and large amounts of down time.
Second is attitude that varies by dealer. A customer centered service department is to be treasured. If the goal is to end with a satisfied customer, the work usually ends up being top notch. Contrast this with the mechanic that gives a huge shopping list because its a slow day and he wants to stay busy the rest of the day at your expense.
Last is the dealer working for you when there is an issue with Nissan. Its no joy when there is a problem and you find yourself against both the dealer and Nissan Corp. Thats where the lawsuits come to play. When the dealer sides with you, Nissan usually will follow the lead.
Some love their dealer, others hate theirs. These are the reasons why. Domestics have an advantage because if your not satisfied, its usually a very short trip to a good dealer. Competition is a good thing. Imports normally have fewer dealers and fewer options for the owners.