I think the 777 will in fact go down in history as the greatest commercial aircraft of the post-747 era.
Long story short, the 777 has allowed airlines that did not have a market for the 747 to resume ultra long haul service. Just think, Delta, for example, could order the 772ER and serve the ATL-HKG market. That particular market would usually have to connect through SFO or LAX. No longer.
The 777 is just as important a development, if not more important, than the 747. Why? Because the 777 changed the way Boeing, the world's leading aircraft manufacturer, builds its products.
The reason the 777 is such a quality product is because of what was just stated above. The 777 is the first ever commercial aircraft that is built exactly the way airlines want it built. Everything, from the location of the fueling door to the material from which the ailerons were made to the toilet seat that doesn't slam down, is just the way airlines wanted it.
I don't think Boeing will be able to do this with the 747X. They couldn't with the 764 or the 73NG because they were based on old designs. Not that they are bad airplanes, they're just not as good as the 777.
That's why it's inevitable that the 777 has and will continue to cannibalize the 747's market. I suppose you could say that Boeing designed too good of an airplane.
It's a new day. Every moment matters. Now, more than ever.