According to my GPS, the last time I rode OBW, I covered 13.1 miles. I rode the two trails, parking near and starting at the Fire Tower, without getting on the Adventure Trail, which I understand can be "hike a bike" in places.
The new Group Camp trail starts with a weave through the woods, some fast segments, then moves into a rocky, technical section as it crosses a series of dry creek beds, then switches to a mix of rock, roots and some fun rollers as it gets past the Group Camp. It's approximately six and a half miles out and back. I would consider it the toughest trail at OBW, but then I haven't been on the Adventure Trail yet. I haven't been to Brown County either, but I have heard other riders compare it to Walnut.
The Fire Tower Trail starts fast and flowing, with a nice elevation drop. There is one log across the trail that requires jumping, or hitting the brakes, which interrupts the flow. One rock garden hangs right along the edge of a steep hill, which is quite impressive, and provides a strong incentive to clear the segment. After another short mix of flow and rock, it meets up with the Rocky Ridge Loop. The Rocky Ridge Loop starts with a fast, rolling section, then drops into a rocky section as it crosses a creekbed and climbs out, before working back out to the Fire Tower Trail. It's got to be about six miles or so in total by the time you'd get back to the Fire Tower. There are some technical segments on the Rocky Ridge Loop and I personally don't consider it as tough a trail as the Group Camp Trail, but it is definitely not a beginner trail.
There is also an additional side trail that runs up from the start of the Rocky Ridge Loop to the Campground. I've ridden that a few times just to fill my water bottle.
In my opinion, it is definitely worth a visit.
