The only similarities between them is that they came from a group, are "blue eyed soul" artists, and are successful solo artists with their limited catalog.
Justin is a co-writer/co-producer. For the most part, George did everything himself in Wham! and his solo career. One of his albums sold just as much as MJ's, which is unprecedented. His material in a group and solo is MUCH better than Justin's in a group and solo.
George Michael has a way better voice.
While Justin does some writing, he's heavily reliant on his producers. George Michael is more of a musician. Plus he was more of a risk taker. Justin chases trends so while successful, he'll never be considered an innovator.