Not a Sudoku-X puzzle, since only the “positive” diagonal is marked. Still, the unmarked diagonal is interesting. And not just on a global scale!
Rules:
Normal Sudoku rules apply.
Digits within cages sum to the small number in the top left corner of that cage.
The marked diagonal contains the digits 1 to 9 exactly once.
Estimated difficulty: 2 out of 5
Solve on SudokuPad