Sometimes the difference between a three and a four star is a hard one. I think what separates the difference at a museum is one thing - return ability.
The Arizona Science center is some where south of a science museum but makes a decent enough children museum.
The best exhibit for us, actually, was a kinetic/water area as you enter. It was a lot of fun and the only thing that was worth returning to. The air area was very weak.
Next up was a construction area that was slightly entertaining, but didn't hold our interest for long. After that, we moved on to a body area. This is where we spent most of our time. Plenty of interesting exhibits and things for my four year old to interact with.
The 2nd floor had a slightly fun area . . .electrical equipment and the like. The third floor was . . .boring. Thunderstorm, and a small exhibit at that.
The water play area was the highlight. Though my four year old was entertained. . by 2.5 hours we had saw all we needed to see. I couldn't imagine getting a membership here. . .there just isn't enough to come back to over-and-over again.