I've been to Pittsburgh twice, once in 2007 and and another time last Summer. Unfortunately I haven't been able to get up close to both the point where the 3 rivers meet and the huge fountain in that area. If that was open and I was able to stand at the Point of Three Rivers I'm pretty sure it would be a 5 star experience.
I saw the fountain in 2007 from across the river by the Steelers stadium as well as from atop Mt Washington and thought it looked magnificent. However just as I was going to head over there it was turned off for the night, the 2nd time I was here that area was closed off for restoration of the fountain.
Hopefully by the time I'm in Pittsburgh again the fountain area will be open. However even without that this is a neat place, and on my last trip I wen't inside the Historic "Block House" in the park. and was blown away by the interior. How on Earth it's possible for such a small appearing building from the outside to look so spacious on the inside is fascinating. The space has inspired me, really cool and it's free.