Ginny. They give her no personality in the films, she's just an airhead, whereas in the books, she jokes, she lies, she's a bit like a mini twin!

I'd say maybe Ginny, Dumbledore, Cho Chang and also Tonks. I just didn't seem to picture them like what they were in the movies. Dumbledore was great until POA when the new actor came in. It seemed like all of a sudden Dumbledore had a bit too much energy in him. I thought Cho Chang would be a lot prettier. Tonks..was just weird I have to admit. She was the biggest surprise for me and I thought Ginny would have a lot more confidence in the movies.

tonks i did not thinks she would look or be like that

Cho Chang, Ginny Weasley, Dumbledore... And actually Voldemort. These people weren't portrayed the way I imagined them when reading the books.

I don't like the new actor for Dumbledore, I feel like he is always angry, especially in the GoF. I don't, he's just not like the one in the first two films.

Dumbledore. Words cannot express my dislike for Michael Gambon in that role. Angry!Dumbledore isn't canon at all. Richard Harris was brilliant, although I am glad that he wasn't Dumbledore in the 6th movie because I would have cried and cried during the cave scene where he has to drink the potion.

Ginny, obviously. I have nothing against Bonnie Wright though. I blame the directors entirely for completely ruining her character.

I feel like Ron has a lot less depth in the movies. He's just kind of the dumb comic relief side kick. And I know that he is some comic relief in the books, but he's also so much more than that and the movies don't even begin to touch on it.

Ginny. Obviously. She has no personality, no fault of Bonnie's, just the script.

I also think Voldemort isn't. Sorry, guys, but he isn't scary in the films, the amount of times I have laughed at him...

The phisical appearance isn't like how I imagine Sirius Black, but Gary Oldman was apsolutly fantastic Sirius !

Ginny for sure. Possibly Voldemort.

I didn't really like how from the 3rd movie on, Hermione had normal hair...she's supposed to have bushy hair as we all know, and huge teeth until book 4.

Also I thought it was odd that until the sixth movie when she had a larger part, Lavender Brown was played by a black actress, but then was all of a sudden white in the 6th movie.

Going by physical appearance, Emma was a total mismatch. Hermione isn't pretty- she has bushy hair and large front teeth. Emma has played the role to perfection, but looks really very pretty, unlike Hermione.

Ralph Fiennes doesn't seem as scary as he is supposed to be.

Michael Gambon doesn't really seem like Dumbledore. Richard Harris was more than perfect as Dumbledore. They should've found someone more convincing to play that role - someone with a calm expression and a reassuring smile.Gambon has a more 'angry' look on his face.

Ginny is very different in the movies. It's not Bonny's fault, I think the script-writers and directors ruined her role.

Ron has not been given much importance. He is far more than just a comic relief and sidekick, but that's not how he is portrayed in the movies.

I don't think we can say that a character is least like the book version just because s/he is not the way we imagined. Because each person is going to have a different version of the same character in their mind.
Like the main trio, for example. Emma made Hermione a lot more sensitive than I imagined, Rupert made Ron a lot more scared than I pictured and Dan made a... weirdo Harry. Hahahaha xD that's my opinion, of course. It doesn't mean they recreated the characters badly.

But, of course, there are some characters that are absolutely different from their "original versions". Like Ginny, as everyone's saying. She has no personality at all and doesn't have Ginny's power and confidence. Ginny from the movies is just... meh. It feels like she's just there to be Harry's girlfriend and that's it. And Ginny is waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaay more than that! She's powerful and awesome! A female version of the twins! o/