I will be upfront in saying that I have worked for the Arizona Science Center as a Summer Camp Instructor, so my review may be biased.
The ASC has a beautiful facility. True, some of the exhibits are better than others, but each exhibit has a goal of education in mind. I've found that children get the most out of the ASC when their accompanying adult takes the time to talk to them about what they are experiencing (even if it means reading the sign next to the display), rather than just letting the kid run around like a maniac. The ASC also has an awesome planetarium which is definitely worth checking out, along with the IMAX theater.
I most recently visited the ASC for their educator preview of Body Worlds. The Body Worlds exhibit alone is worth visiting the Arizona Science Center, if only to open your mind to the complexity of your body. (Don't be ignorant! Learn something for a change!)
What makes the ASC so great in my opinion is what they do for continuing science education. Have you ever had the opportunity to take a course at the ASC? Or a summer camp? The Arizona Science Center goes out of its way to make it an incredible learning experience for you or your child. They have rooms in their basement packed full with science equipment, alongside other enormous rooms where they build the next exhibit. ASC's goal is to educate Phoenix (children and adults) about science and nature. This means that the Arizona Science Center will continue to grow and prosper as Phoenix does - therefore we can only look forward to bigger and better things!