We have been going to the science center since it's beginning and it is just getting better. SO much to do, so little time. Both children love it there (ages 6 and 10). They are less interested in learning the science of the exhibits than touching them and making them do something but it keeps them entertained. Definitely go to the Planetarium - you don't get to see those everyday. There is an IMAX but we never get a chance to go because we run out of time. The traveling exhibits are great, as long as you don't have to wait in line very long. The memberships are great if you plan on going there more than once like we used to do when the kids were younger - you also get a discount on their summer camps (which are awesome).
Be prepared and you will enjoy it more:
1. It's expensive. There is an admission fee, fees for the planetarium, fees for the IMAX, fees for the traveling exhibits and parking fees (even when validated). You can get discounts occasionally on groupon or dealchicken but plan on spending some dough.
2. It's time consuming. Plan on spending a minimum of 3 hours there. Plan ahead and see what's playing at the planetarium and the times. There are different shows throughout the day. Same with IMAX.
3. DO NOT EAT THERE. There is a cafe but don't waste your time or money on it. It's terrible and expensive. Wear comfortable shoes and walk down to another restaurant for lunch and then come back. OR you can bring food in - there is a huge lunchroom on the side of the cafe for large groups.
4. It can be crowded. Sometimes it's empty, sometimes it's filled with school groups. If you are not in the mood for crowds, you might want to pick another place. If you need a stroller, and it's crowded, it's a nightmare.