Cedar point is terrific. Kings island near Cincy is a distant second, but it's still a solid park.
If all you want is an amusement park. Sandusky is nothing to write home about. You're pretty close to Cleveland but there's nothing to do there. I'd take an extra half hour and drive to Columbus instead. Or if you wanted to make a weekend of it, check out put in bay (as long as you're in season). It's like a redneck Mardi gras there.