Heinz Hall is excellent!
Inside, it's ornate and beautiful in a way newer facilities can not replicate. Red velvet seats, gold-accented ceiling, etc. is everywhere you look.
Acoustically, it's very good, a little resonant, and very quiet. As expected, front-of-balcony is probably your best bet for hearing music (a.k.a., "dress circle" tickets).
You can see the stage well from just about every seat. The only negative I've noted is a lack of knee room for taller patrons. Not a huge deal.
I think it's a treat just to spend time inside this great music hall.