What is (so special) different about Dzogchen? In relation to the comment in this answer '... regular Buddhism is college - Dzogchen is like a PhD.' Also, Sam Harris seems to endorse Dzogchen.

I am reading online like the wiki page etc. Does not seem to be any massive difference or something out of ordinary. 

Can somebody please explain.
Dzogchen teaches a non-dualistic state of one's own primordial nature, with nothing to reject or accept, that is pure from the beginning in the nature of a light body. -- Khenpo Palden


In simple words:

Original Buddhism introduced many new concepts to describe 1) the unenlightened state of mind, and 2) practice leading to Liberation. Theravada's approach is to preserve these teachings as closely as possible without alterations. From Theravada's perspective it is the student that must adapt to the Teaching - not the other way around. So the student is expected to learn the exact original definitions, ideally in the Pali language. However, for many students this approach makes it difficult to see the forest behind the trees.

Mahayana Buddhism prefers to stay away from repeating the rigid concepts from Pali suttas and instead tries to re-tell the same meaning in its own words. This is why Mahayana often prefered writing new texts instead of quoting original suttas. So Mahayana's approach is more focused on conveying the "point" of the Teaching, rather then the "letter". In Mahayana, the teaching adapts to the spirit of times and places, to explain Dharma in the way the students can relate to. Still, just like Theravada, Mahayana Buddhism is mostly about 1) the unenlightened state of mind, and 2) practice leading to Liberation. But this is not all there is to Dharma, it also has the third part: Result!

In Dzogchen speak, the three parts are called Ground, Path, and Fruition - and Dzogchen focuses 100% on the third. Truth be told, some parts of Mahayana like Madhyamaka do approach Fruition in their teaching about Emptiness - but they mostly try to explain it conceptually, in terms understandable to the unenlightened mind. In contrast to that, Dzogchen directly teaches how the Enlightened mind sees and acts. Dzogchen focuses directly on what it feels like to be Enlightened or to be in Nirvana. After all the teachings of Theravada and Mahayana are learned, and all the practices fulfilled - after the Raft has been used to cross over to the other side and left behind - what remains at that point? That's what Dzogchen is about.

So Dzogchen is even more "to the point" than Mahayana - in its purest form it throws away all those teachings and explanations, and goes: "here is what Enlightened mind is like, now you do it". This is what makes it so radically different from everything else.