At first I didn't know what to think of him. After all he was made out to be the bad guy who messed with Sasuke's mind. However, I found it strange that the perfect son would suddenly go crazy and slaughter his entire clan, save for Sasuke, so I didn't know what to think of him and didn't form an opinion about him until I saw his face when he heard that Sasuke could have possibly died during the fight with Deidara.
I started to respect him a bit because he believed in his brother and he got my full respect after Sasuke's fight with him.
Now he's placed in my top ten favourite characters, though he isn't perfect