R.E.M. - written off for dead by many critics after releasing three consecutive albums that failed to live up to commercial expectations - added yet another chapter to the year's most convincing comeback story during its thoroughly entertaining show on Saturday night.The Athens, Ga.-based group delivered a fiery, inspired two-hour performance, consisting of 27 songs, which reminded the 8,500 fans at the University of California's Greek Theatre in Berkeley exactly why they fell in love with R.E.M. in the first place.