These trails rock. There is something for everyone although, not too much for beginners, unless you like eating dirt. The trails are great with a lot of ups and downs. Long ups and downs for Michigan. Mostly hard pack dirt and some mud holes at the bottom of the hills other than that, it's dry most of the time. I've ridden there quite often and never saw another rider. Some equestrian users now'n then but that's it.
There's a few lakes the trails wrap around which makes for some good scenic riding or a place to take a swim and cool off. I love the place and always look forward to taking a ride there when I'm in the area. If you're in the area or just looking for a new trail its worth a look. Otter lake has a camp ground and food supplies. I don't know of any local bike shops so bring your emergency kit(spare tubes etc).
How to get there:
Take Willard Rd east, from M15 and stay on Willard Rd until you come to the Michigan State Game area parking area on your left. I guess you could call that the trail head. If you keep going you'll run into the end of the road, turn around and the parking area will be on your right. Unless you have 4wheel drive this is about the only place to park.
This is a state game area, so stay out during hunting season. The lakes got good fishing too :)