some of his major policies can't be judged until 20-30 years from now
however, death of Bin Laden, no economic crash, supreme court justice nominations that helped legalize gay marriage, some of his policies re: the middle east can be considered good things for him
also, his administration emerged scandal free and he is perceived as competent, which will ensure his legacy remains positive. He wasn't out here getting head like Clinton or wasn't a blubbering idiot like GW Bush.
In terms of legacy, his floor will be Bill Clinton (loved by his own party, hated but respected by his opposition), and depending on how his policies turn out, he could be the Democratic version of Reagan (his party admires him like a god, even 30 years after his presidency)