Ridiculously beautiful!! There are unfortunately much fewer official trails for mountain biking than I would have wished, but *whispers* I went on all the trails anyway. Outstanding how massive this State Park is, its beauty, amazing facilities, signage, and pathways. I would highly recommend this to cyclists that want a mixture of paved and dirt/groomed grassy paths. You really need to be cycling in order to see the entirety of this huge park, which is why I'm so sad that cycling is not condoned on all paths. If it's a weekday I'm sure you can get away with it, but likely not on a weekend.
I would recommend if you're just visiting for a day, going all the way to the end and parking where the rental bicycles are; this will help you to know where everything is (I was lost when I first entered). Then cycle up to the woods North of there where the pretty cabins are and entering the woods from there. There are many paths that are missable without a careful eye. Cycle all the paved paths and roads in this park so you can find them all! Have a blast!! Many great fishing spots too.