The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people
-The Tenth Amendment
Well gee, who knew States had rights. Raise your hands if you did. See we live in a country where there is a clear succession of Government. Local, State Federal. Well obviously the laws that work for a small state like say Rhodes Island, are not going to work for say Alaska. It would be absolutely insane to have laws regarding say Bears in Hawaii, and laws about Whales in New Mexico. But its also kind of insane to have a federally mandated Minimum wage. Or there should be a minimum you can possibly earn, but that should never be set by the Federal Government. Why? Well for the same reason that Federal Edicts about speed limits make no sense. If I say that the National Speed limit is 45, that the speed limit for all roads is 45 just averaging out residential streets and Highways, well that makes so many problems its not even funny. I'm sure someone could potentially be barreling down a residential street at the speed limit and run over little Suzie and her bike and not even notice it till it was all over. Conversely well, if all the interstates are reduced to 45 MPH it would take hours to get anywhere let alone long distances.
The States also need to be protected from the Federal Government. Ever read Atlas Shrugged? In the first part of the book Colorado is experiencing a boom, so to "normalize" the rest of the country a special tax was placed on Colorado, and also some other schemes to suck the state dry to "give to the more needy States". I'm not going to spoil the book for you but it actually backfires. This idea that one subordinate Government needs to be protected from its higher government is actually pretty new.
I personally believe that this Amendment is quite important and that the 17th Amendment destroys a lot of the power that the States did have (more on that later). But a quick quiz, what is the "State's House"? If you said the Senate you are correct. Indeed the Missouri Compromise was all about retaining some semblance of parity between Slave and Free states in the Senate. Hell the stated reason for the secession of the South was for state's rights. Their constitution almost guaranteed the government would fail, but that's beside the point. After the Civil War the issue of State's Rights was put to bed or so it had seemed, until just very recently.
Now with Obamacare the 9th and 10th Amendments have become somewhat of a focal point, for the legal challenges. More so the 10th Amendment, several states (more than a third actually) banning together in some cases, others going it alone, but the entirety of the Law is being challenged on the grounds of the 10th Amendment. I would have liked more challenges like this when the Great Society or the New Deal came along, but you can't always have what you want.
Now to be clear this Amendment does not state specifically any rights that the States do or do not have. It is left to the reader to go back and check that everything is in order, and it is assumed that the States would watch the Federal Government through the Senate to make sure that nothing unscrupulous was happening with Federal Power (thus partially why the 17th Amendment is a bad thing). All 50 States have their own unique history and problems. Even within the States there are Laws and problems that aren't being handled very well. This tends to happen in say Illinois or New York or California, which have such massive cities they can simply out-vote the "yokels" in the rest of the state. However when the Federal Government comes down from on High and Declares something it tends to be bad for the State, and Local Governments. As the saying goes Shit rolls downhill. Eventually the Individual will feel much pain from such Federal Edicts.
My Take: This Forgotten Amendment should be the rallying cry of Governors everywhere. Our Government is too bloated to sustain itself, and while many states have problems and issues of their own if they do not start controling their destiny and soon the whole system will collapse. America is unique in this way. We have a "Chain of Command" in our Governments, and it is important for any American enterprise that the loyalty be both ways, or else the system will fall apart.