We stayed at Rocky Neck Park for 4 nights, and I don`t really have any complaints. We stayed in the Osprey Loop which is full shade and was nice. The campsites aren`t too crowded, and many do have trees in between you and your neighbors but they aren`t super spacious or anything. It seemed to be more crowded in some of the other loops though. This didn`t really bother us though as our neighbors were polite.
The beach here is nice but nothing special, it is a little walk from the campsite but nothing bad at all. It is on the Long Island Sound, so there are barely any waves if that is what you are looking for. It can get very crowded on the weekends though. There is a concession stand open most of the summer I believe. Be warned that the Amtrak train does pass over the beach and it is very loud if you are not expecting it!
The bathrooms seemed to be well kept, and you can buy firewood near the entrance to the park. The only thing that may be bothersome is there was quite a few bold skunks that were walking and running around, and they would get pretty close to you! They didn`t seem to be too phased though, and nobody was sprayed or anything. Not sure if this has changed as I visited last year, and it may only be in the wooded campsite loops like Osprey that have to deal with it. Once you got used to it, they usually retreated into the woods fairly quickly when shown the flashlight.