How much have you looked it up? Do you know what's there and just want recommendations on what's worth the time, or are you looking for a general overview or...?
Right now there are mainly two categories of 50th stuff: merchandise and food. I can tell you that the big show stopper for Epcot is a whole Aztec pyramid made of chocolate sat atop a tres leches cake with ice cream served in Mexico. I have yet to try specifically it, but I can tell you that I go crazy for the smaller version of that cake normally served there (it usually has sweet corn ice cream; I don't know if the big version has that or vanilla) and recommend it at every opportunity.
(I can also tell you that the Epcot Experience's cronut is not worth the money.)