I was waiting for others to comment. Wilderness is a great park with electric only, dump station, and water fill at the dump station. The section of park near the lake is smaller sites while the wheel area away from the lake is for larger units. In May you could have very cool weather which means jackets yet no bugs.
You are only a short distance from a Dark Sky park great for stargazing. Mackinaw, the island and other tourist things are nearby.
In May you probably won't need reservations unless you are hitting a holiday.
Have a great time.