Galactus destroys all of Asgard as well as the entire universe and drinks Odin's blood in the mean time.
Seriously think about it. Odin's domain lies on an asteroid in OUR solar system being powered by OUR sun. Galactus is a universal level being that can decimate the entire universe 10X over. Odin shouldn't be as powerful as he is, much less be in the same thread as Galactus. Odin would have trouble beating a 15-20% powered up Galactus let alone a 100% Galactus.
Galactus takes this fight anywhere, he's just that damn good. People fail to realize that Galactus is kin to Death, Eternity, and Oblivion thus this puts him on there lv.
That brings up one question for me about Cyttoraks power. Cyttorak in Sorcerers Supreme #49 was able to imprison Galactus inside his dimension. On another occasion Eternity made an attempt to get rid of Cyttorak and failed. So where does this put Cyttoraks power?