Good puzzles, you did great job!
But there are some interesting oversights worth mentioning.
First of all, game have some problems with WinXP(that's not the issue, just part of the story) - it crashes when you enter the middle door. So I entered the left door, not knowing about shift mechanics... and I managed to pass it :) The Mirror Guy doesn't reset his position after The Normal Guy's death(and vice versa), so I easily moved him down from his platform. Then comes the tricky part. When you move and jump, The Mirror Guy bumps his head into the ceiling and stops or just slows down, but The Normal Guy is still moving, so distance between them grows. So I passed this level that weird way. Only then I decided to read comments and discovered about shift mechanics :)
But more than this, then I tried to go through all levels without using shift, and yeah, you can do it :)