This is the third in a series of three puzzles which get progressively more difficult. Finish the first puzzle for a link to the second puzzle, and finish that one for a link to this one. Which you already have, clearly.
Rules:
Normal Sudoku rules apply.
Killer Sudoku: The digits in each cage sum to the small number in the top left corner of that cage.
Estimated difficulty: 3 out of 5
Solve on SudokuPad