Warriors of Rock is the last in the GH series, Activision deciding to axe the series, likely due to Rock Band taking all their sales. Aw with most of the Guitar Hero games, WoR adds a whole new slew of songs you can choose from, being shipped with 93 at release and plenty more available to download, and it continues to offer all the different instruments mentioned above. It is worth noting as well that the appearance of the game has improved, but not massively.
In quickplay you can play any song you have unlocked or purchased, either on you own or in a band with friends on the same console or even over Xbox Live. Each instrument has its own challenges to aim for for every song, as does playing as a band. It's still a staple of the series' feel that it's a game you get out while your friends are over or at a party.
Again as with the other GH's, there is a campaign mode. In WoR it adds some new gameplay mechanics but unfortuntely for some reason they have made it single player only, a loss in gameplay from the previous games! The addition is 8 powers, 1 for each character/stage in the campaign, which you unlock through the campaign but again, even in quick mode, the powers can only be used in single player. They add things like a higher point multiplayer or a shield against missing a note, which are pretty good but don't really make up for the loss of the band campaign.
Quite a short review, but then there isn't much thats changed from the rest of the series. I've not done a multiplayer section as technically there isn't one, but you can have other players join you over Xbox Live for quickplay as I've said, they even got rid of the battle mode from the earlier games! The powers are fun, but as I've said quite restricted, however despite the loss of content the game is still worth getting for playing the wealth of good rock songs in quickplay with your mates or over live.