"Solve a series of spatial puzzles in a short window of time"? Is there some kind of timer? Good spatial puzzles don't need timers. Putting a timer on puzzles says "My puzzles are crappy, so I'll just add difficulty by not given you enough time to complete it"....

Have played through the first 4 or 5 levels and on 2 of them a piece disappeared. In both cases it was a smaller piece that was supposed to go all the way in the back. I believe it clipped through the wall. Anyways, it's a bug and it feels bad when you think you've completed the puzzle but then it gives you an error and you take out pieces one by one only to realize one of them has vanished into thin air....