The LR is a fine aircraft by today's standards. But the 787 will set the bar higher, and will be a fine aircraft by tomorrow's standards. At that point the 777 will be the prior generation, kinda like the way most of us look at DL's 767s today.
A big factor is environmental responsibility. If Boeing delivers on its promise, and there is no reason to believe they won't, the 787 will burn about 20% less fuel on a per passenger basis than the current generation of aircraft.