It's a national landmark and an amazing engineering marvel.
Normally something like this wouldn't impress me quite as much, but when you think about how this dam is 75 years old, yet still produces as much power as it does and still has no equal to compare it to, it just adds to its grandeur. I can't even imagine how much a project like this would now cost and how long it'd take (it took 5 years to plan and build Hoover Dam).
One thing I wished I looked into before would be online ticketing. I don't know why I didn't think of it, but it's definitely available. I only did the generator tour and I think that's probably where the most interesting stuff is; however, don't take my word for it since I haven't done the "full" tour.