Kisame: Hard to pick something not to like. . I mean, i think he's a fairly well rounded character. But I'd choose. . His over all 'Okay' to Obito's plan. For some one like him, I thought it'd take more convincing.
Nagato: The way he originally died was bad. I would have liked him to either be introduced earlier or have lasted longer, past that arc. Expanding his character more.
Anko: Very weak, and I would have liked it more if she fought more like Orochimaru. Would have been sort of neat.
Tayuya: She died. I disliked that.
Kimimaro: He also died, and I think he could have been so much more.
Kabuto: He was always cool, but when he got Sage Mode we was awesome! But. . I think he could of handled his last battle better.
Orochimaru: The fact that he used Edo Tensei to fight Sarutobi, would have prefer'd him using different techniques and actually fighting.
Madara: His attitude, how powerful he is, he broke free from Edo Tensei. His attitude both annoys and attracts me, I think at a certain point he shouldn't treat everyone like shit and a man like himself would show the Kage's more respect. He is WAY to strong as an Edo. I don't think he should have the Rinnegan. . .Just don't like it. And he just broke free from Edo Tensei. . . I think that should have been it for him.
Zabuza: For the best assassin in the show, he made a pretty dumb move in his last living fight with Kakashi. Why didn't he make more water clones and chip away at Kakashi like that? Or try to imprison him in the water sphere again and then have a water clone run him through with Kubikiribōchō.
Haku: He could have killed Naruto or Sasuke. . If it came down to serving Zabuza, I think he would be willing to kill. Also, why couldn't he paralyze Kakashi with a senbon to the neck if he had time to run over there? He was a VERY skilled kid, after all.