woo hoo! as late 20-somethings even we had fun here! we swung by since we have city passes but unfortunately arrived with only an hour to spare! parking's typically $8 but we got lucky and no one was manning the parking booth. we quickly entered and were amazed at how large this spot is! at least 3 floors full of interesting, fun exhibits! there are areas to learn about the human body, psychology experiments, forensics, nature, space, physics... just about anything science and it's there! i dispute claims that it's better than the exporatorium in SF - while the are around the exploratorium is nice and the tactile dome can't be beat the ontario science center is HUGE and has at least 3 times as many exhibits!
the most popular machine was probably the aging machine that can take your picture and show you what you may look like in 50 years. even though the museum was about the close there was still a long line to have photos taken.
granted, when this spot is stuffed full of kids fighting to try experiments it probably isn't quite as much fun as what we experienced (since almost everyone was gone we got to run around and play with whatever exhibits were available). if you have a kid they'll LOVE it here and i can definitely see how if you live in the area it'd be worth it to get an annual pass.