In 1951, The Day The Earth Stood Still meant something. The Earth was done with it's Second World War, but the aftermath left the world in conspiracy and distrust. With the world so completely torn apart, what would happen if we were visited by alien life? Alien Life clearly more powerful than us and whose intentions are unknown?
Klaatu comes to Earth to let us know that our hostile ways will not be tolerated. The Universe has learned the consequences of aggression and war and that peace is the solution. But Klaatu is met with opposition, restrainment, and eventually death. Klaatu is revived and presents his ultimatum to earth. You can fight amongst yourselves, but aggressive against other planets will result in your planet's destruction.
1951 was the perfect time for a message to mean something. 6 years prior, the Atomic Bomb detention in Hiroshima and Nagasaki showed the Earth how destructive we can be to our own people and our own planet. At that time, everyone was scared it would occur again.
In 2008, we've arrived at a different message. We're killing our planet. Humanity has proven too irresponsible to exist on Earth and must be removed. There are so few planets in the Universe that can sustain complex life. It's been decided that the Earth cannot be lost.
This message would probably be "profound" if it wasn't already being broadcasted everywhere we look. Being Green, Hybrid Vehicles, Reduce, Reuse, Recycle. I think we're already in consensus that we should stop trashing our planet.
In 1951, the message of the film was controversial. Anti-Communism movements were rampant in the US. It was us versus them. The film broke those boundaries. In fact, the National Film Registry has preserved the film as being "culturally, historically, and aesthetically significant" according to wikipedia. The Day The Earth Stood Still meant something.
2008's The Day The Earth Stood Still is simply preaching to the choir and thus means nothing.
In Addition, 2008's Day the Earth Stood Still tries to be too many movies at once. It tries to be Sci Fi and Disaster and Thriller and critique humanity at the same time. The movie is completely split between the US Government trying to disect Gort while Keanu Klaatu runs around with Jennifer Connely learning about humanity and vading the cops.
It tried to cover way too many angles and became a gobbled mess by the end.
On the other hand, though, I thought the Sci Fi elements of the movie were pretty rad. 2008 Gort is amazing. Klaatu's spacesuit shell and healing properties were neat, too. Though, the electricity powers were a little much.