Every 9x9 box is a valid sudoku, making 9 sudokus in all. I'm not sure how hard it is as I started solving it with just a few clues, then added more whenever I got stuck. Enjoy!
It is in fact much easier than most normal sudoku puzzles.
For example, the rows 1 2 3 in column 1 are 1 3 4, which tells us that the rows 10 11 12 in column 1 are also 1 3 4, in some order.
This gives us much more information than it appears.
For example, the column 10 of row 10 is 3, so in the columns 1 2 3 of row 10, there must also be a 3.
Combined with the last piece of information, we conclude that row 10 column 1 must be a 3.
With this kind of logic, I solved the whole puzzle without any of the tricky logics used in normal sudoku puzzles.
However, as the puzzle is huge, it is really labor intensive and very easy to make mistakes. I had to roll back several times because of errors. Other than that, I would say it's an easy puzzle.
Nevertheless, I appreciate the effort put into creating it, and I hope to see some more tricky versions. (But perhaps slightly smaller in scale?)