Music games are a big deal. In under three years, the genre has become the biggest segment of the video game industry. Kai Huang, president and co-founder of Guitar Hero originator RedOctane, a division of Activision Blizzard, says in a phone interview that the category’s sales were $250 million US in 2006, and he expects the number will top $2 billion this year.

The two biggest players in North America are Guitar Hero, and Harmonix-MTV Games’ Rock Band (distributed by Electronic Arts). This despite the fact that Konami essentially invented the rhythm-music category with games such as Dance Dance Revolution, Karaoke Revolution, and GuitarFreaks and DrumMania, released in 1998 and 1999 respectively.

The Guitar Hero and Rock Band franchises are also being credited with saving the music business. So much so that Metallica — who refused to release their music in digital form, even suing fans for sharing music — have reversed their opinion and embraced Guitar Hero World Tour (PS2, PS3, Xbox 360, Wii; rated teen) and Rock Band 2 (Xbox 360 version available now, PS3 on October 19, PS2 and Wii on November 18; rated teen).

The success of the genre has inspired every game developer and publisher to crash the party. This fall, Konami is introducing Rock Revolution and Disney Interactive has Ultimate Band, a Wii game, which uses the controllers to play drums and guitars. Nintendo has its own music game planned — Wii Music, from Mario creator Shigeru Miyamoto — but comparing it to Guitar Hero or Rock Band is a stretch. It’s more of a music toy than a game. Players simply mimic playing instruments while holding the remote and nunchuk controllers, pushing buttons at will while the game plays the actual notes.

Despite the influx of competitors, the real competition in the music game category this fall (at least in North America) is between the Guitar Hero and Rock Band franchises.

While Guitar Hero got the party started, Rock Band pumped up the volume by letting gamers sing and play drums in addition to playing guitar and bass. This fall, Rock Band 2 differentiates itself with a deep and extensive catalogue of songs. For a small fee, all songs from a gamer’s Rock Band playlist can be imported to the sophomore edition of the game. This means a library of nearly 300 songs, with more being added regularly. Harmonix expects more than 500 songs in the library by the end of 2008.

Guitar Hero World Tour, which adds drums and vocals to its game with this latest iteration, is looking to user-generated content as a way to set itself apart. Among World Tour’s features are “music studio,” a way for gamers to compose and record their own songs, and “GHTunes,” a way for those personal compositions to be shared with others.

The instrument controllers for both games are now wireless and more sturdy. For those gamers who like to bliss out on every music game possible, the PS3 and Xbox 360 versions of Guitar Hero World Tour, Rock Band 2 and Rock Revolution (Konami) will be compatible, so the drums and guitars from one game will work with the others (although the controllers from one system, will not be compatible with another, so don’t expect to use your Xbox 360 guitar on a PS3). Konami, in fact, isn’t even producing a guitar controller for Rock Revolution, expecting that most gamers have at least one in their possession already. This means that Guitar Hero fans can easily add Rock Band 2 to their game library, and vice versa.

Guitar Hero and Rock Band have also put to rest the stereotype of video games being a solitary pastime. These games are social machines that provide an opportunity for people to come together to celebrate the shared experience that is music appreciation. Even professional rock musicians relax at the end of a long day by playing Guitar Hero and Rock Band. However, a rhythm and music game is only as good as the songs it includes. In an interview with Fast Forward, Harmonix vice-president of product development Greg LoPiccolo said that his company, which develops Rock Band, is “like the curators of rock.”

The tracks included with Guitar Hero World Tour and Rock Band 2 are all taken from master recordings of original songs, as opposed to remakes, with the exception of the Sex Pistols songs, which were re-recorded because their label reportedly lost the master tapes. Both games provide a mix of genres as well as tracks by artists who are not found on the other game. World Tour is the only game to include Jimi Hendrix (“Purple Haze (Live)” and “The Wind Cries Mary”), Tool (“Parabola,” “Schism” and “Vicarious”) and Van Halen (“Hot for Teacher”), while AC/DC (“Let There Be Rock”) and Bob Dylan (“Tangled Up In Blue”) fans will be laying into Rock Band 2.

In addition, Guns N’ Roses’ new track, “Shackler’s Revenge,” from the long-awaited Chinese Democracy album, will debut on Rock Band 2.

Also included with Guitar Hero World Tour are songs by Billy Idol (“Rebel Yell”), Bon Jovi (“Livin’ On a Prayer”), The Eagles (“Hotel California”), The Guess Who (“American Woman”), Michael Jackson (“Beat It”), Nirvana (“About a Girl (Unplugged)”), R.E.M. (“The One I Love”), Sex Pistols (“Pretty Vacant”) and Willie Nelson (“On the Road Again”).

Other Rock Band 2 highlights include Blondie (“One Way or Another”), Dinosaur Jr. (“Feel the Pain”), Elvis Costello (“Pump It Up”), Jethro Tull (“Aqualung”), Journey (“Anyway You Want It”), Modest Mouse (“Float On”), Sonic Youth (“Teenage Riot”) and Rush (“The Trees”).