If you enjoy simple puzzle mechanics that lead to very challenging logic puzzles, then check out Zen Puzzle Garden: http://www.lexaloffle.com/zen.php
. The basic mechanics are extremely simple, but you'll be surprised at how many rich and interesting puzzles arise from them. It's a very bare-bones puzzle game, so don't expect any story or anything. But the presentation is very soothing and contemplative and very appropriate to the game. So, strap on your thinking caps and give it a whirl. There's a demo.