tsk tsk, orochimaru is indeed evil and takes over people's body for power buy he's the sort of evil whose's plans keep being stopped. I consider Itachi to be more evil than Orochimaru, one he's ruthless and doesnt care for talking much before a battle. It's either you attack me or i'll own your ass the moment i move. He's just one of the strongest and dangerous S-class missing nins ever. Combined with the fact that he has the Sun God sharingan move, no one can defeat but a skilled blind fighter. He's that dangerous, Orochimaru fears to meet Itachi and that why he's got sasuke waiting for him to be taken over. His Sharingan may be able to resist Itachi but we dont know since we only seen a pre-time jump scene between them where Sasuke got owned. Itachi will kill a baby without hesitation if it meant success to his assignment.