Full of stars, Rhode Island's avoided by festival critic (8)
I believe the answer is:
'full of stars' is the definition.
'rhode island's avoided by festival critic' is the wordplay.
'rhode island' becomes 'ri' (US postal abbreviation).
'avoided by' suggests deleting specific letters.
'festival' becomes 'gala' (a gala is a festival or party).
'galacritic' with 'ri' removed is 'GALACTIC'.
(Other definitions for galactic that I've seen before include "Relating to large star systems" , "Of independent system of stars in space" , "More than stellar" , "Of large independent system of stars" , "Relating to, eg, the Milky Way" .)