With the recent destruction of azaroth at the hands of deathwing, the ensuing cataclysm has changed most of the zones in Azaroth with the shattering patch, which has run upto the release of Cataclysm, which will finalise the expansions changes.
With this expansion, not only has blizzard added new areas, but also completely changed the old content for the better, with this expansion you have hours of new content, and the new ability to fly in Eastern kingdoms and Kalimdor! Yes, you heard me right.. you can now fly everywhere, as long as you are level 60 and have the ability to fly in azaroth.
So, why is this the best expansion yet? It's because it adds a ton of content, it may not have a new world, or continent like BC and WotLK but it has made so many improvements and the new zones are bloody fantastic, and this is coming from someone who has played on the beta, that it justifies not adding a new world or content, the amount of detail and effort that blizzard has put into this expansion is staggering, and i highly recommend everyone (Not just those with a level 80) to get this expansion, to have every feature this expansion is adding, including the ability to fly in EK and Kalimdor, as well as the new profession Archeology as well as to become an illustrious grand master at a profession.
I have given this 5 stars, and it's worth everyone of them.