Our day arrived at last. The experience is pretty much what the name suggests. You're not going to find the sustaining intellectual nourishment available at many other SF museums, but you will get a completely enjoyable sensory and sugary overload. My daughter and her friends absolutely loved it. I enjoyed it too although as we progressed I found myself more in the role of jacket/camera/purse carrier so they could run amok.
When you get there you will see a line outside, it moved pretty quickly and I got the sense that they were more worried about capacity than anything. We arrived a bit early for our 2:00 slot but they let us in around 1:40 or so. It took us about an hour to go through. They don't rush you and you will spend a good bit of time waiting for people ahead of you to finish their photos. In general you can't go back to previous rooms. Some rooms have selfie stations where you can email yourself stills and videos. There are bathrooms about halfway through. There are some bottlenecks in places like the unicorn room and before the sprinkle pool. (I can't believe I just typed that last sentence.)
Random observations:
We have a small bowl filled with some of the plastic sprinkles from the "pool" that managed to make their way to our house despite our best efforts. You'll be finding those for weeks. You'll also notice them on the ground for blocks around the museum.
They will tell you you can ask for seconds but it's easy to forget since it's so visually overwhelming. But yeah, you can ask for seconds.
Try all of the mochi flavors.
You don't have to put the whole bag of Pop Rocks in your mouth at once. But I did, just saying.
At the very end they have ice cream you can buy, which was the last thing we needed at that point. I would have gone for a jerky stick or something.