Ring Sudoku [WSC 2013]

[Fred76]

23 - ring sudoku.png (175.88 KiB) Viewed 72734 times

Source: 2013 WSC, Beijing

More than the particular example, the question is about geometry of the grid.
Here in my opinion all properties are met to say that this puzzle is a sudoku. However, the geometry is unusual (in this particular case, it can be cumbersome to perceive sets formed by rings). Does someone have limitation for sudoku concerning geometry, or is the limitation only at the discretion of the author?

[detuned]

I think it's certainly a very poorly designed variant - the constraints of the geometry mean that it isn't really possible to get anything approaching an interesting solving path...