There is, however, a dark side to all of this: Unless you're a genius, some of the levels are guaranteed to make you angry. For example, one particularly epic (and frustrating) stage near the end forces you to build a staircase by fitting together irregular blocks, build another staircase going down and then dodge a flashlight guard while carrying weights from the beginning of the stage to a pressure-sensitive door near the exit. This level is emblematic of PQ's chief flaw: While it's addictive as hell, it takes a long time to muddle your way through some of these puzzles, and undoing 10 minutes of work by accidentally stepping in front of a guard or a laser is the sort of thing that induces psychotic rage.
Checkpoints would solve this, although that would probably be cheating. Interestingly enough, though, cheating is easy: once you've run down the timer and your moves trying to trial-and-error your way through a level, simply quit the game and restart the level. Provided you don't make any more mistakes, you're brilliant (at least as far as your score is concerned).