Not a bad trail. I biked a lot of it. Considering it's length, I would suggest doing that if you're looking for a short trip into nature. It's a short drive from Portland and a nice area. Not a lot to see if you spend your time hiking it in my opinion.
Regarding the Townsite Trail near the actual park, I've always enjoyed this quick and easy walk with my dog. I let him off leash often and let him scout a few feet ahead of me. However, the mosquitos are bad at certain times of year - wear sleeves, scarf, and bug spray.