I remember being a young kid, under five-years-old, going here and riding on the large locomotive and walking through the larger-than-life model heart. I went back to the Franklin Institute again twenty-plus years later, and while these things seemed small than I remembered them, they were still there and still as enjoyable.
Even though these staples are still there, the place has changed with the times. For instance, when I went there as an infant, the computer era was also in it's baby stages. However these days they have a large area displaying computers and allowing people to check out the internet. I guess you could even write your Franklin Institute entry from inside the Franklin Institute! I also seriously suspect the environmental issue is new or has been renovated to reflect a more Earth-conscious population. When I was last there, they were re-working the trains/steam engine area. So while I could see the engine I remembered, I couldn't stand on it.
One of the new things I wan't able to try, but looked like a lot of fun, were the sky bikes. These are scientifically-safe version of a carnival tight-rope bike above the main hall.
I thought the hall of astronomy could use a face lift as parts of it seemed outdated.
There's a lot of hands-on things throughtout the whole Institiute. More so than most museums I can think of. Kids and adults will have a ball. Speaking of which, there was a sports exhibit up (I don't know if it was permenant) where visitors can test their skills in various virtual sports environments.
Ticket prices depend on what you want to do. I think general admission was like $9, but you add on things like laser-light and planetarium shows and the skybikes.