In the end, the decision lies on whether or not players can discover their inner classic rock fan and if they don't mind the disc isn't a full game. There isn't a lot to be found on the disc itself but the proven engine of Rock Band 2 is still there. To break it down, players are getting $40 worth of song content for $10 less and the allure of 250 more achievement points isn't too shabby either. If you're into expanding your Rock Band experience, the disc will do exactly that, however, if you're looking for a marathon Rock Band outing, the expansion is only meant to extend your enjoyment of the main series.
You'll probably only get a couple of hours out of the disc before you're ready to move on, however, the now-standard download code will let you take the disc's offerings into the robust world of Rock Band/Rock Band 2.