It is very busy. At opening the line will be long, on busy days we plan to park the car 5 minutes after opening. They are not very fast at opening. We go to the left, past the water park and start at the lightening racer and work our way to the front. We leave the park around 2pm to avoid the worst of the crowds. During non-holiday weekends we would go back after 6pm, we would never go back on a holiday weekend.
The comet and coal cracker can (not to mention skyrush) get really busy. We go to those first on the second day. We do notice that coal cracker will sometimes have no wait before closing. It is a slow loading ride.
We really like Hersheypark and have had annual passes for several years. If you have the extra cash (325 ish) you could rent a cabana in the connected water park and just deal with the crowds.
We like to eat at hersheypark park place, have some wine, if nice sit outside. This is outside the park at the entrance. For fast food we like mixed grille express and always save room for a Rita's ice. Outside the park we like piazza sorrento.
Lastly, giant grocery stores will usually have Hershey's on sale, much cheaper than the store. Not as a fun, no singing cows.