A game is an RPG when nobody appreciates it, instead choosing to look through rose-tinted glasses at its increasingly archaic predecessors.
More seriously, they're games where you chose how your character grows, both in terms of story and gameplay.
Although to be honest, whether or not a game is an RPG shouldn't be the point. We should be trying to make good games, not trying to make sure that they're technically RPGs. People ask 'is ME2 a real RPG?', as though it's a sign of quality. They should be asking if it's any good; besides that, genre is hardly relevant.
More seriously, they're games where you chose how your character grows, both in terms of story and gameplay.
Although to be honest, whether or not a game is an RPG shouldn't be the point. We should be trying to make good games, not trying to make sure that they're technically RPGs. People ask 'is ME2 a real RPG?', as though it's a sign of quality. They should be asking if it's any good; besides that, genre is hardly relevant.