There's an unspoken, freefloating notion that online "casual" games are some strain of second-citizen entertainment -- doubly so for anything considered "kid-friendly." Though the stigma is often deserved, Peggle from casual powerhouse PopCap Games is one of those happy, rule-proving exceptions. It's part billiards, part pinball, part pachinko, part philosophical eye-candy reflection, two parts superb polish and layers upon layers of subtlety, replayability and (occasionally-maddening) challenge. When Einstein said "God does not play dice with the universe," he was talking about the apparent, unseemly randomness implicit in the then-new field of quantum mechanics, not video games. However, had Einstein been into games, he'd likely have backed the idea that God does play Peggle, or something very like it, with the universe.

Each of Peggle's levels follows a formula. Easy-on-the-eyes background artwork (themed to one of 10 host characters), a ball-launcher at the top of the screen, a playing field filled with color-coded, pachinko-style pegs (along with occasional barriers and/or moving targets), and a ball-catching bucket moving back and forth across the bottom of the screen. The basic idea is to pick a launch angle, send the ball bouncing and jouncing and pinging and ponging from peg to peg (clearing said pegs, making the playfield that much sparser -- and harder), collect as many points as possible through foresight, skill and sheer, drooling-idiot luck, and maybe even pot the ball in the roving bucket below for a extra/free ball. Once you determine the launch angle and make the shot, the only thing to do is watch for cause-and-effect -- but you can't call it a luck-based game.

An introductory Adventure mode gradually introduces new players to the base mechanics, point-snagging tips and tricks, and, most importantly, the distinct power-ups offered by each level's host. What begins as a cute and seemingly luck/fluff-based "casual-gaming" time-waster gradually reveals bonus layers of challenge, complexity and replayability that absolutely dwarf the main gameplay mode (no easy feat itself).

And like other deceptively-simple, deceptively-kiddie-looking games -- the brilliant Worms series comes to mind -- Peggle is very easy to begin playing. It's also very easy to convince yourself by the end of Adventure Mode that you know what you're doing. After all, you've mastered bank shots off the screen edges, right? You've managed to clear all the pegs, right? Bah. Each level completed is later thrown back in your face with a new challenging twist. Get all the orange pegs, for example, get all the pegs period, score 250,000 points, score 350,000 points, clear the screen --with only two shots instead ten! In fact, the bonus challenges go on, ramping up in difficulty until they seem impossible, but there's always a way to pull it off. Think, dammit, think.

By the time you hit the levels of seemingly-endless Bonus challenges, it's all about your eye for angles, your predictive skills, and the crazy power-ups offered by the characters. One offers a "Spooky Ball" that makes a second pass at the screen to Tocatta and Fugue in D Minor. Another spins a carny wheel for bonus shots, multi-balls or triple points. One detonates all nearby pegs in a "space blast." Still another simply "zens up" your initial angle for the best foreseeable short-term flight path. Some of them are invaluable for certain levels, while others seem useless, but eventually you'll find a reason for resorting to most of them at least once.

Finally, the level of obvious pre-release playtesting, balancing and general polish in Peggle puts many big-name console developers to shame: Graphics are flawless, audio is crisp and clear, the physics are amazingly fluid... all this in a game that exudes challenge and tension despite "controls" that consist largely of a single mouse click per level. Amazing.