I disagree with gray that Legendary items suck. But I do agree with him to the extent that Blizzard's implementation has something to be desired. It's certainly not how I would be designing acquisition of these types of weapons. I like the idea of legendary weapons being the result of truly epic quest chains but I don't like the idea that they are tied solely to raiding, and I definitely don't like the idea that they are so easily outstripped by higher ilevel weapons. If I had my way in this I'd instead make legendary weapons truly legendary, starting with making them all exceedingly rare. Quest chains for legendary weapons in my WoW would begin with random drops that start a year long or more chain of events that require some group activity but which mostly would require a lot of solo effort. And my legendaries would upgrade over time, similar to the heirloom gear now. Perhaps not automatically but there should be a means to upgrade them for each tier.
As much as I would love Shadowmourne right now on my Paladin (I'll never see it), it saddens me that in just a few months better weapons will be available anyway.