I find everything about park skiing hard. It takes me a long time to learn most tricks. I have to extensively visualize anything I want to learn, and then spend a lot of time learning all the parts of the trick, so it requires a lot of motivation for me to progress.
I haven't had access to a very good park for any length of time, and my ski season has always been about 3 months, so your resources can really affect your skiing.
"Cross training" is really helpful though (mountain biking, skateboarding, climbing, swimming).
I also enjoy skiing out of the park more and more as time goes on.