If World of Warcraft wasn't a big enough timesink, now we've got Sudoku! Oh crap. The puzzles are just so bloody addictive. Check out the web version.
What makes it such an interesting game is its paradox: how can something so simple be so devilishly complex. When the human brain encounters such things, it goes into over-drive and the desire to resolve the paradox becomes overwhelming. Well, at least that's how it is for me.
