The aggressive marketing of the Beatles catelogue remasterings (including those dozens of favorable reviews that have been appearing for the last week or so). The sound is unmistakably improved over the 1987 CDs, like everyone’s been saying. To my ears the bass and drums are the most enhanced. Plus you can hear dozens of little other little grace notes and consonants and tonal effects much more clearly.
The sum effect isn’t stunningly different — you’re not going to be staggering out into the street going “what happened? I just listened to the remastered Revolver and I lost all sense of tiem and space!” — but the CDs (individually or in a package) are surely worth the purchase. And I’ve been telling myself for the last two or three years I’ll never buy another CD again. Never say never.