if you like roller coasters, it's probably the best in the country. When I lived in MI, I used to go there every summer. It's right on the lake too, so if you're making it a destination it would be worth renting a boat or a jet ski or something and having a day to relax in the water. There's also an attached water park, but it's a separate admission.
I wouldn't drive that far for any amusement park; but if you're looking to road trip for some roller coaster fun (or just in the area) Cedar Point is the place to go.