Wow...I completed it on my first guess. I'm not really sure how to explain, but I'll try.
Hints:
There is an 'x' that goes from each of the corners, which helps form one of the 2x2 blocks in the very center. The top left corner is also filled in with a 2x2 block. The next 2x2 block starts at R1C6. The last 2x2 block hint starts at R4C9. The puzzle is symmetrical on the diagonal axis.
I ended up getting a few different solutions apparently? None seem to be it (i didn't fully understand the hint kind of orz but it helped me get one of the wrong solutions?
Hints:
There is an 'x' that goes from each of the corners, which helps form one of the 2x2 blocks in the very center. The top left corner is also filled in with a 2x2 block. The next 2x2 block starts at R1C6. The last 2x2 block hint starts at R4C9. The puzzle is symmetrical on the diagonal axis.
Hope that sort of helped.