Hersheypark does get crowded at peak times of the year, but it is usually pretty managable. Like everyone else always preaches (because it's true), get there early.
A good plan of attack is to get Comet, Storm Runner and Great Bear out of the way first. Sooperdooper, Lightning Racer, Wildcat, and Trailblazer are usually pretty managable anytime during the day. However, Trailblazer can get a little interesting if they run one car.