This was actually my fourth or fifth trip to the museum, and it continues to impress. The exhibits are really extraordinary. My personal favorite is the cab-forward steam locomotive, with is truly awesome. They've opened up the cab for display as well, so you can sit in the engineer's seat and get a real feel for what it was like to drive this monster! The rocking 1930's Pullman car is also a real treat. For kids of all ages, the Lionel and Buddy L toy train exhibit on the second floor is incredible!!
The only negative comment I could make is about the movie. It's so California-politically-correct it's almost laughable. It's also due for a remake, since it's the same one they've been showing for many, many years.
That aside, this is a really great museum for the entire family. And as one other reviewer said - plan on setting aside plenty of time. There's a lot to see!!!
Highly educational, and highly recommended!