Depends entirely on your terminal
The AirTrain links the terminals and connects you to the subway and rail into Manhattan.
The experience swings wildly by terminal, and some feel dated and cramped.
JFK is really several airports wearing one name, and your day hinges on which terminal you land in. I found the staff a bit brusque and one terminal noticeably tired compared to another I'd used before. The AirTrain is handy for getting around and into the city, which softened the rough edges.