Newark is a really nice airport. Especially Terminal C. There are good site to spot within the terminal and because the airport's area is fairly compact, the runways are fairly close to the terminals, which allow for really good spotting. Terminal A is not so nice. I haven't been there since they revamped Terminal B and added the monorail. As well, the city is around the airport so the take-offs and landings allow for some really breathtaking views of the New York/New Jersey area. Most of the international flights leave in the early evening, so if you want to see diversity, wait 'till then, otherwise it's dominated by CO. And the horrors about delays are true. The airport is totally overcapacitated. I have been victem to EWR's delays.
The city itself is not so nice. Newark has the reputation of being the carjacking capital of America. Crime is very high and it's really dangerous to go out at night, and maybe during the day. NJ could have changed as much as New York, but I don't know. You should have a blast. The NYC metro area has loads to offer.