This is an amazing trail system. The parts on the North Shore near the stadiums are really nice and open. I've run north past the casino and science museum once and some parts of that trail are a little isolated. Also a lot of gnats!
On the other side of the river, the section from Smithfield Bridge to Hot Metal Bridge is pretty nice, but again, there are some sketchy sections where you are very isolated and it looks like some people live there by the river.
On the Eliza Furnace portion between Hot Metal Bridge and 2nd Avenue, there are some portions where you are close to the highway so the noise and the fumes are not awesome but it's great that this trail exists.
You can literally run miles and miles along the rivers in Pittsburgh, across bridges and through the heart of the city. The city is lucky to have such a wonderful asset and I try to run these trails whenever I'm in town.