Orochimaru is good at Genjutsu. it is just Itachi is Master of Genjutsu, unlike Oro many other Kage lvl Shinobi wouldnt even be able to move their hands like Orochimaru did. he would probably break out of it, that is why Itachi stopped him.
The reason ppl say that Oro is weak against Genjutsu is that only he lost against Genjutsu and u know why? only he was brave enought to fight against it. for ex look Deidara he got negged so hard he didnt even realize that he was in Genjutsu he didnt even move inch, unlike Oro who was moving his hands and was about broke it, i think that this is great feat to fall in Itachi Genjutsu and able to move ur hands. look at Ay he got negged by Edo Madara's Genjutsu and if not Onoki he would be dead, Cee, Ay's bodyguard who is Genjutsu user negged by Sasuke, Kurenai Got negged by her own Genhutsu lol i am not saying anything ab Bijjuss.... now tell me how is Orochimaru bad at Genjutsu when he has best feat against it.(i dont count Sharingan users Vs eachother well u know reason why....)
