The people who created Shotokan Karate did not necessarily expect it to be fun. I doubt they imagined that it would become a World Wide activity with tournaments and seminars. The original purpose was to protect the Emperor of Okinawa and his family. They had to dispense with their enemies quickly and effectively. The original training was brutal and produced microfractures in the hands/wrists, feet/toes and shins.
In today's society, the training has inevitably changed. No one wants to live with the arthritic changes, degenerative joint disease and pain that repeated injuries produce. However, a traditional Dojo is still possible with a strict training regimen and requirements. There can be fun in the discovery of techniques, sparring and working with a trusted partner. But, with that being said, the discipline must remain intact and the standards of performance must be maintained.
The Shotokan we practice today is most certainly very different than that of the developers of the style. In the West, people do have very different expectations. Fun can be part of a serious school, especially in the core upper belt students. What is seen as fun as a beginner, will be different that what a Black Belt may see as fun. Black Belts may create fun in their classes as they become free to explore techniques and counter techniques. Even the fun that Upper Belts have, must still show discipline and committment.
If you are in a Traditional Dojo, fun is not the goal. In fact, I have heard High Ranking Martial Artists say, "If the Dojo you train at is fun, you are in the wrong Dojo."
The bottom line is, there is a time and place for fun. Every class will be different. You as a student have to show up ready for whatever your Sensei has planned for the class with a willing attitude and a heart to do the hard things as well as the fun things.