Blank Slate: Neat idea, but I found it pretty tricky and annoying to time all lemmings, so that they don't splat in the digger tunnel and arrive (as a group!) when the digger is almost finished with his work.
Act Fast: Very good level that was lot of fun to play.
Silent Circus: It shows that this level originally had a different solution.
Trap Well Sprung: Good level. I first thought that walkers may just walk over the rock (with only the right-hand side being too steep) and therefore went for a completely different approach (using two bombers to create a path from the bottom platform just over the water to the platform with the rock).
Threads of Life: My solution is very likely not 100% intended.