I have a number of friends who are currently in the MPA program. They all enjoy it, but the workload is intense. You will probably spend many a nights in the basement of Robertson Hall. (I know I did when just taking summer courses there.)
As far as nightlife, have you ever been to Princeton? I am pretty sure the only chain establishments in the city proper are Starbucks, Panera, and CVS. Everything else is locally-owned establishments, which is great, but it is a small town. My friends hop on the train to New York and Philly often. There is also a bar on campus just for grad students.