If you start down by the water, the hike is a good moderate uphill trek. Only downfall for me was the water treatment plant around mile 1. Kinda smelly and gross while you're trying to breathe and legitimately exercise. Other than that, it's a decent paved trail with a lot of people.
I have to say, the description of this trail is off a bit. First of all its not a six mile trail. It is a 3 mile paved trail that you can go out and back on to make into 6 miles if you want to. It is open to walking, running and biking all the same. If you walk or run the trail, I recommend staying on the right hand side as bikers tend to go through this trail at a pretty good clip. Second, the singletrack mountain biking trails on the north end of the park (more than 4 miles in my estimation) twist and turn and cross in so many places I've turned this into a 13 mile hike myself. What I'm saying is, there is lots of room to customize this system of trails to whatever kind of activity or workout you want. Keep in mind, if you plan to use the mountain biking trails there are no maps to help you. Furthermore, there are also no signs anywhere in the trail system. I would not let that scare you off, just leave yourself extra time to explore.