Since I'm not a young teenage girl
(teasing!!!
) this really won't be about who looks good and not . . . it'll be more about talent.
). Maggie Smith is just a fabulous actress, and she brings a wonderful understated quality to any role she plays, in my humble opinion.
I also think Tom Felton is wonderful as the nasty Draco . . . not only does he have the little snarky vampire look I envisioned, he brings a lot of personality to the role. I don't feel this yet (though, I did more in the second movie) with Daniel Radcliffe as Harry. Harry has some intense and heartfelt moments coming up in movie three, so I hope he's able to be a little more expressive.
I love the faces Rupert makes as Ron, and perhaps, even though Daniel seems a little flat, Rupert seems to make up for that, so in scenes together, it actually works--I *love* the car scene in the second movie!
Emma Watson is how I imagined 'know-it-all' Hermione, and switching back to professors, who couldn't laugh at Kenneth Branaugh's portrayal of Professor Lockhart?!
I will say a lot of these characters, though, are much funnier and outrageous in the books!
It'll be interesting to see how the new Dumbledore does . . . on the whole, I prefer Dumbledore in the books. Love Robbie Coltrane as Hagrid, and though I love to hate the Dursleys anyway, they did cast them well!
What are your thoughts on the actors who play the HP characters? Whose portrayals do you like and dislike and why? 
Oh, and I also loved the Weasley twins! they are soo damn awesome! Even though the boks says that they shouldn't be so tall etc, I that they, and Ron too are just pefect for the roles!!!