Designing a puzzle game

http://www.scottkim.com/thinkinggames/GDC00/bates.html

http://devmag.org.za/2011/04/16/how-are-puzzle-games-designed-introduction/

http://en.wikipedia.org/wiki/Puzzle_video_game

http://devmag.org.za/category/development/game-design/puzzle-game-design/

Designing enemy units in games

Here is an interesting link on how to design your enemies

http://www.gamasutra.com/view/feature/131735/designing_enemies_with_distinct_.php?print=1