Brad's review touches upon the visceral reaction of the player once he is sucked into the babe-magnet-maker that is Guitar Hero. However, cool as it may be to have a tool to be a groupie-getter, there is another point to Guitar Hero—it's also about making music.
As he said in his GameCritics.com interview, Alex Rigopulos' primary goal in crafting his games (other than EyeToy: AntiGrav) is to make the act of music-making accessible to any gamer due to their unique skill set. As a musician of 22 years, I agree with his statement that music making is a fundamental joy that every human being must experience. Guitar Hero brings that joy to many who wouldn't ordinarily be able to pick up a guitar and whack away at Black Sabbath within a couple of hours.
What makes Guitar Hero different from almost every other rhythm action game is the basic control mechanic. Harmonix has made a game that actually feels like one is playing a fretted instrument. As such, a player has to learn how to play "properly," as he or she would a real instrument in real life. And just like real life, it's impossible to play the harder modes without practicing the easier songs. While this fact is usually the death knell that heralds the end of music lessons as a child, it's totally appropriate for a videogame.
The realistic feel of Guitar Hero is achieved two different ways: the controller and the level design. The guitar controller layout mimics the feel of the guitar really well. The sensation of the guitar in your hands only furthers the belief that it's not just a game, but a performance. What is most surprising is how natural it is to pick up and play. Virtually anyone with a modicum of rhythm can survive the easiest levels.
However, in order to complete the harder levels, there is one technique that must be learned: the hammer-down. Essentially, it involves plucking only once with the right hand, but fingering multiple notes with the left. Any guitar player worth his weight knows that picks can only go so fast. Guitar Hero has the player using hammer-downs to not only enable them to play more notes, but also to dictate the musical quality of the melody itself. This is how the level design contributes to the realism. Drawing from real fingering patterns, the button presses for each song are very close to what is actually played on a proper guitar (albeit with some creative license for only five buttons). Between main melodies, chords and hammer-downs during fast solos, the fingering patterns feel completely natural--especially for those who've played a real instrument.
Playing music is not a passionless activity, and here is where Brad's emotional reaction to the game actually comes into play as a proper technique. At a rock concert, a guitarist holds the guitar more vertically than horizontally when he gets really pumped (at least in the '80s). Guitar Hero encourages this feeling by having the player tilt the guitar controller upwards once a gauge is built up. Suddenly, the lights shine extra bright, everything is aflame, the volume is turned up and you're the star, rocking harder than before. Playing the right notes suddenly isn't as important. All that matters is you, your guitar and the music. You ARE the Guitar Hero. The primal instinct that tends to take over most players is used to its fullest advantage, making PS2 guitar-playing that little bit more real, even down to "faking" the solo in Hero Mode if the need arises.
In fact, the only downside to the guitar is the whammy bar, which doesn't affect much of the game. Though it sometimes looks like it increases your score slightly, its gameplay impact is marginal. It's only there for the realism of guitar-playing. Considering how minor this complaint is, it doesn't have a negative impact on the experience whatsoever. Besides, it would destroy the illusion of playing the guitar if it weren't possible to bend notes like crazy. And as Brad wrote, the song list is missing a few notable tunes.
But those points are trivial compared to what is there. And what is there is incredible. There are many music games, but few of them hold a candle to Guitar Hero. It's easy to say why it works, but it's better to experience it. It's both technical and visceral, conscious and unconscious. To put it bluntly, it's playing music. With Guitar Hero, Harmonix has fulfilled its mission statement.