I did the A loop on foot last weekend and really loved it. It's made up in a small area so typically you would be circling in the same area with pretty much the same views throughout which was a little disappointing especially because i like my trails to have a view at the end. Loop A was 3.8miles plus a 0.1mile from the parking lot so typically you would be doing a good 4 miles.
I agree with the advice of taking precautions for bugs and mosquitoes but that's everywhere.
If you are looking for a good weekend workout within an hour of Detroit this is the place to go!