1. His annoying-as voice. The way he says 'Master', among other words, drives me crazy!
2. He thinks he's so awesome, the way he thinks he is better than Obi-Wan, he can rival master Yoda as a swordsman, and he is madami than ready to pass the trials. If he was, he would learn to control his anger, and not be so angry with Obi-Wan and the Council
3. He is too angry. His line in episode III: "I HATE YOU!" to Obi-Wan was completely unreasonable. Can anyone tell me why he would have reason to say such a thing? I would pag-ibig to hear your explanations.
4. I understand his committed pag-ibig to Padme, and that is why he turned to the dark side, but surely there was a better way to do things! He would have to be pretty weak to believe Sidious!
Well, that is all I can think of for the moment, but if I think of any later, I'll post it in the comments. Please remember that this is only my respectful opinion, and I would pag-ibig to hear other peoples opinions, disagreements, etc. (Kindly, though, please)