I did a little bit of research after my last comment and found that 2 million is about the average number of guests any of the Legoland parks get each year, with Windsor being a little bit higher. In Windsors opening year I also belive that number was only 1 million, which was the most successful launch of any of the Lego built parks.
2 million for a new park is a very ambitious target, especially given the Japanese park is by far the smallest. Not to mention they only opened in April, meaning they missed out on several months of operation.
It would be interesting to see how much revenue they have made on merchandise, as I belive that is the most profitable aspect of Tokyo Disney.