This week, Activision rolled out “Guitar Hero 5,” the company’s latest salvo in its ongoing battle with original “Guitar Hero” software gurus Harmonix’s rival “Rock Band” franchise.

At this point, the full-band music game genre is pretty well defined: Players sing, strum or drum along with pre-recorded music using instrument-shaped controllers (except in the case of the singer, who uses an actual USB mic). You’re graded on how accurately you can press colored buttons along with on-screen cues.

With the exception of “Guitar Hero World Tour’s” music-creation software, which lets gamers write instrumental, MIDI-based songs and share them online, Harmonix’s “Rock Band” franchise has been a more of an innovator in the full-band genre, with the first “Rock Band” having beaten “Guitar Hero World Tour” to market by a year. Innovations like an in-game song download store, allowing users to rip music from “Rock Band” to their hard drives for play in “Rock Band 2” and a general polish have left Activision playing a bit of catch-up. (For what its worth, Activision seems to manufacture better instruments.)

That said, “Guitar Hero 5” brings a number of new modes and features to the table. For starters, a drop-in/drop-out party mode lets you use the game as a sort of jukebox. It’ll play music from the game disc at your party, and folks who feel like picking up the controllers and playing along can do so. The game also allows four gamers to play in any combination of instruments. Got four kids who all want to sing? No problem. All you need is four microphones. (I shudder to think of the noise complaints those four-drummer bands will generate.)

The game’s also the first one in the genre to let your Mii and Xbox 360 Avatars appear on stage playing the songs in place or alongside the game’s created and unlockable characters. I’ve seen gameplay footage of the avatars playing along with “Guitar Hero” characters and honestly, it looks kind of weird. I’d probably rather create a rocker in game that matches the look of the title, but you can’t fault Activision for giving players the option.

Perhaps the coolest new addition to “Guitar Hero 5”  is an innovation first pioneered by Harmonix. Like “Rock Band 2,” “Guitar Hero 5” is the first game in the series that’s backward compatible with downloadable tracks from the previous game. In other words, if you shelled out $50 downloading a bunch of songs to play in “World Tour,” they’ll work in “Guitar Hero 5,” as well. What’s more, if you own “Guitar Hero World Tour,” you’ll be able to download 35 of that game’s 86 tracks to play in the new game. It’s not as good as a percentage as what “Rock Band 2” players got. (Only three songs from the first “Rock Band” weren’t playable in the sequel.) But it shows Activision has been paying attention, and it’s a great start. (And no, you can’t play “Rock Band” songs in “Guitar Hero” or “Guitar Hero” songs in “Rock Band.” Both companies work out their own licensing agreements with the music companies and barring some sort of historic merger or earth-shattering development in the arena of copyright law, the two games will remain very separate entities.)

Additionally, “Guitar Hero 5” features an updated version of “World Tour’s” song creation software, as well as Rockfest, a new mode that lets players compete against one another rather than play the game’s signature cooperative mode.

On the “Rock Band” front, MTV-owned Harmonix and its partner Electronic Arts haven’t announced “Rock Band 3” yet. Instead, they’ve been focusing on “The Beatles: Rock Band,” which releases Wednesday. That game, which is made up entirely of Beatles songs and tells the story of their career, is more of a standalone title. It brings a number of new features to the genre, such as the addition of three-part vocal harmonies, but you won’t be able to export its songs for play in “Rock Band 2.” It also won’t feature support for other “Rock Band” tracks you might have downloaded. This no doubt has something to do with the legal agreement MTV signed to get Paul McCartney, Ringo Starr and the widows of George Harrison and John Lennon to agree to let their likenesses be used in the game. (You could see why Paul McCartney might not want to see the Fab Four playing Guns N’ Roses’ “Shackler’s Revenge,” for example.)

Anyone worried Harmonix is moving away from cross-compatibility, however, should be assuaged by the recent announcement that songs from “Lego Rock Band,” due out this fall, will be playable in “Rock Band 2.”

As for the mythical “Rock Band 3,” details have been scarce, and Harmonix and MTV seem content to innovate via free downloadable updates for “Rock Band 2.” The biggest of those, the Rock Band Network, could shake up the music game genre considerably when it debuts this fall. (It’s reportedly currently in beta.) The Rock Band Network gets around the fact that MTV can only sell new downloadable songs as fast as Harmonix can convert them into note charts. The plan is for Harmonix to train a number of third-party contractors who will then work with music companies to code the tracks up themselves. Once finished, the songs can be sold for anywhere between 50 cents and $3, allowing record labels to make a wider selection of songs available at a variety of price points. The service will initially be available on the Xbox 360, with plans to roll out popular songs to other consoles at a later date. Independent label Sub Pop (Nirvana’s original record label and home to artists such as Sunny Day Real Estate, Velocity Girl, The Shins and Band of Horses) has pledged to be an early adopter.

“Guitar Hero 5” (rated T) is available for $60 as a standalone game for Xbox 360 and PlayStation 3 and Wii, or $40 on PlayStation 2. A bundle including a guitar costs $90 for the PS2, $100 for the other systems. A full band set and a bundle featuring a new drum kit will release later this fall, although the game’s drum parts are playable with drum kits from other music games. As stated above, early buyers of “GH5” will get a free copy of “Guitar Hero: VanHalen” when it releases around Christmastime.

“The Beatles: Rock Band” (rated T) is due out Wednesday. It costs $60 as a standalone game for Xbox 360, PS3 and Wii. For the moneyed, a $250 special edition bundle that includes replicas of Ringo Starr’s drum kit and Paul McCartney’s bass guitar, plus a microphone and mic stand. Replicas of the guitars of George Harrison and John Lennon are sold separately for $100. A special $160 “value edition” includes the game and a drum kit, guitar and microphone from the first “Rock Band” game.