The trail is a very easy singletrack and the Heart Healthy Loop is all easy fire road.
If you stick to the Blue Heron Trail then there are some annoying parts through parking lots and a stretch along some roads. I'd recommend avoiding the part at the end of Vine Rock Street as it's very overgrown.
Overall, a very easy trail although with some good long boardwalks to traverse. Nothing too steep (up or down) but plenty of rolling with the trail; in fact, I think you could probably do plenty of it with no pedaling at all! The Heart Healthy loop around the pond is a wide fire road with a couple of off-shoot trails that take you up and down the bank.
Parking is super easy, and if the lot is full the kind folks at PTC (the adjacent lot) let you park there on the weekends (please be respectful of their space though!)