The feedback s very much appreciated. I think an undo function might this game of puzzler a little bit. I'd guess the annoying part you found annoying was in the last level where you have to do quite a few steps before you get to the juicy part of the level, which really likes to destroy atoms and I totally agree that there's a problem/flaw in the level design! In a revisit of the game I'd also replace the destroy mechanic with respective ones that just block movement.