The simplicity of the system - a score per peg, multiplied by the amount of pegs hit - was intuitive, and allowed for an exponential increase in score for a cunning (or, let's be honest, lucky) shot. The scoring in Peggle Deluxe was perfect. It's so suffocatingly basic, you'd need something special to bring it out of mediocrity. You only have control over two things: which direction you launch your ball, and when you launch it. Once the ball drops out of play, the lit pegs disappear, and you shoot another ball. Bonuses are awarded for slides, trick shots, and blind luck. Purple pegs give a score boost, and green pegs activate the special power of the character you're using. Orange pegs are the ones you have to clear to progress.
Fire a ball into the pegs, and the pegs light up. It was that cocktail of psychological components that makes casual gaming such a lie of a phrase. It wasn't just the basic bagatelle mechanic that made everyone fumble about in their trousers.
It's easy to underestimate PopCap and the year it spent painstakingly creating a version of pachinko that would work outside of the arcades. "Little old uncool us?" I continue to imagine them saying. I like to think that, when Valve joked that The Orange Box was delayed because everyone was playing Peggle, the PopCap staff fluttered a paper fan to their shy faces, and giggled.
I like to think PopCap was surprised when Peggle Deluxe made the leap from casual moneyspinner and guilty pleasure to industry-wide disease.