Impressive, but less impressive than I expected. I think part of the problem is that in the post 9/11 world they don't let you go to some of the places to really assess the enormity of the project.
Here's some advice I wish someone had given me before I went on the tour. They have a mandatory introductory movie before you do the tour. Both the $11 and the $30 tours take it. Sit to as far right of the room as possible. After you finish, they take you out of the door to the right and into one of two elevators to do the tour.
They count the number of people who go through and limit the size of each group as to not overfill the elevator. I was one of five people who did not make it into the first or second elevator. They said we would have a 10-minute wait.
They lied.
I spent almost a half hour waiting in an ugly lobby with no view until the next show let out and our tour could continue. Needless to say I wasn't in the best of moods.
The sights are impressive. Like the huge pipeline for the water. And the enormous generators. I did the $11 show and I can understand now why people would be disappointed with the $30 ticket since they don't let you visit the base of the dam any more.
It's also nice how they don't mince words about the number of people who died making the dam. That's a part of history I think people overlook.
I went on a Friday when it wasn't that busy. I suspect this place ia a zoo on weekends and holidays and I'd suggest not going then.