I needed about 2 levels to fully understand the rewind mechanic. After that I started each level by thinking how is this dev fish going to try to screw me over. I am happy to announce that I had conquered one level on the first attempt.
One small thing I would like to criticize. The blood splats you're leaving behind make for great danger markers for your next attempt, but when you press restart you splat into some blood leaving a mark behind, where there was (in my cases) no actual danger. I can imagine that could lead to confusion and frustration in some more complex levels.