I used to ride my bike from shorewood through downtown multiple times per day and loved the change in environment throughout. It goes from suburban feeling to urban to woodsy and back to urban and it is nice if you're not looking for that solitude. I like that i've seen some weird creatures on this trail as well.
If you are looking for that solitude there are points along the trail were you can veer off and get down to the river and sit on the banks and watch ducks or herons or the strange river creatures. If i was a mountain biker i would definitely explore doing that because I once found some kids with their BMX bikes in this dirt area jumping hills in the trees off the trail.
I ran this trail several times while preparing for a marathon. While it is rumored that the trail will provide more off-road pathways in the future, at this time it seems that the much of the trail follows city streets. It is mostly flat, paved, and does have a nice off-road stretch along Lake Michigan (Bay View) as well as the Menomonee River (Wauwatosa). There are other runners on the trail, but it is is largely used for biking.