ORLY, Orion?
GH: M does improve upon the full band model introduced to the series in World Tour. The graphics on premade characters and venues are a significant step up, and player made characters don't have to be as ugly as they were last time around due to some revamps on art and customization. You don't have to play every song in the game to finish the tour and get achievements this time around, which is a good move considering the blistering speed and intensity of some of the early Metallica tracks (those are the best ones, btw). A few minor tweaks to the multiplayer makes Live play more fun as well, which would be great if more players were online.
Which brings me to the one downside to the game.... with a focus on Metallica and metal, this game won't appeal to everyone, and may not have the longevity of gameplay of a more diverse game (and one that *ahem* supports DLC). However, the upgrades and improvements showcased here show promise for future GH games, which Activision will continue to deliver until the well runs dry.