Simple 1: 100% is possible.
Simple 6: The first very good level.
Simple 9: I just made all lemmings from the upper hatch builders until the gap was bridged, which resulted in a rather uninteresting solution.
Simple 10: Faaaaar too many builders: 7 suffice.
Simple 13: Can be solved using only two skills.
Simple 14: Good level, but needs some tweaking to enforce a really interesting solution.
Simple 15: Even I can save 0%

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Complex 1: Rather uninteresting solution for a level showing so much promise.
Complex 2: Can be solved using just 20 builders and no digger.
Complex 6: By far the best level

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Complex 7: Far too many skills.
Complex 11: A trap has its trigger area slightly above the ground, while one would expect it to kill walking lemmings.
Complex 13: Good level, though RR-fiddling necessary.
Complex 14: Another level with a major backroute. 97% possible.