Very unintuitive plane control. It's more frustrating than satisfying to solve the puzzles. And whenever I do, I'm just glad I solved one and then another weird level that requires knowledge of octagons or 8-cycle loops, or 2x2 squares or 4-cycle loops. Both of them are hellish patterns especially when heavy crates are in the level – balancing the plane is one requirement, but so is getting not only the crate goals, but also the plane goals.