Curiously my most linked-to article ever is the one measuring the size of Azeroth from the World of Warcraft as 80 square miles. With me planning to play more Lord of the Rings Online than WoW in the future, you could expect me measuring the size of Middle-Earth next. But I don't have to, because the size of Eriador, the region of Middle-Earth you can visit in LotRO has been officially announced, and no lesser medium than the New York Times.
They first had the size of the LotRO world given as "50 million acres", which would have been 1,000 times larger than Azeroth. That frankly would be impossible. So they issued a correction stating that they made an error, and that the real size is 50 million square meters, which is less than 20 square miles, and thus just a quarter of the size of pre-BC Azeroth. I can believe that number, I once ran from Ered Lindon to the Misty Mountains, and it wasn't all that far.
Now if you take the size of Eriador and assume that the rest of Middle-Earth will have the same scale, the whole world of the Lord of the Rings Online, after all expansions are out, will be as big as World of Warcraft before the first expansion. Fortunately we can expect Turbine to bring out expansions faster than Blizzard. But criticism that Lord of the Rings Online will be relatively small on release is certainly justified.