Quadrophobia

It’s less common in the world of Sudoku, but many pencil puzzles have a “2x2” rule, although most of those involve “shaded” and “unshaded” cells. We don’t do shading in Sudoku-land, so it’s Odds and Evens instead.
You can shade or color it if you like, so long as you break up every 2x2 set of cells.

Rules:
Normal Sudoku rules apply.
No 2x2 set of cells contains only odd or only even digits.

Estimated difficulty: 1 out of 5