It was a beautiful, warm (for spring) day! If you are meeting anyone there, I would suggest deciding on exactly which trailhead you will be meeting at, as there are quite a few different ones! We parked at the Mercer Slough Blueberry Farm. It has parking, trailhead access, a working blueberry farm, bathrooms (open late spring through fall). The blueberry farm has U-pick berries (in season) as well as seasonal produce (not open yet). So if you decided to do this when the blueberries were ripe you could double a nice urban hike with a berry picking day! The trails were a little muddy in spots, but we were able to pick our way around the mud most of the time (I would recommend boots or shoes that can get dirty if you go when it is wet).
There are several different looping trails for a total of about 6 miles. The trails are a variety of dirt, peat moss (and mud), boardwalks, and gravel.
Not much elevation gain, just a pleasant urban hike/stroll through a wetland area, forest and working farm with a view of the Bellevue skyline in the background.
Check out my blog posting for a full report and more pictures:
http://ahomeschoolmomshikingblog.blogspot.com/2011/03/mercer-slough-nature-park-trails.html