Voldemort is not a very interesting villain IMO. He's deformed, has a hot temper, reacts on impulse, rules people through fear and intimidation, and has a very bland background. Bad-hearted-orphan-kid-who-creeps-people-out.

I think a "good" villain is more than just an angry face and always-pissed off. There has to be more to it than that. Darth Vader and Harvey Two-Face was once good, but became evil after their loved one dies through the indirect decisions of the protagonists. To me, that's kind of interesting. Severus Snape, who starts off as a jerk, we later learned was actually on Harry's side the entire time as a double-agent. That's pretty cool.

Voldemort lacks all these things. Yes we get a brief glimpse of his abusive childhood, but that's become so cliche'd IMO. Why is Voldemort bad? His father was mean to him when he was a kid. Okay. Sure.

I feel that if Voldemort was more level-headed in his temperment and swayed people to his side through persuasion and charisma, it would have been a far more terrifying villian, because he doesn't rely on threats and force, but intelligence. Even in history, Adolf Hitler was able to convince a nation of people to make him Chancellor by appealing to their desires. I think it would have been cool if Voldemort's character wasn't so one-sided.

I also think that his physical appearance shouldn't have been so blantly obvious about this evil nature. "Look at his reptilian nose and bald head... you can tell he's the bad guy!" No. C'mon. Imagine if Voldemort instead looked like this

I also have a similar opinion on Draco Malfoy's character. It would have made him more interesting if Harry and Draco had at least one moment of mutual understanding. Even for just one brief chapter in the book. Instead he's just an annoying character who's only role is to provide inconvenience and taunt Harry into making poor decisions.