I thought Ginny in HBP was just a complete disaster to be honest, they obviously had no idea what to do with her character and made a bit of a mess of it. If they'd bothered to make Ginny's gradually more outgoing personality a bit earlier (eg from GOF-) I think Bonnie would've been able to make her performance a bit more real and audiences would've been able to identify with her more.
Bonnie's finest moments in the HP films have been very subtle, my favourite being just as the DA are leaving the RoR before Harry and Cho kiss, and Ginny just looks back and Bonnie shows an entire character in a shot of about 2 seconds long. Amazing! And quite similar to the little hints in the books of Ginny's feelings for Harry while he's distracted by Cho.
And about the Dumbledore debate? I was very much Team Harris as I thought he was very much the character from the books compared to Michael Gambon. But in HBP however, I adored every moment of Gambon's performance and it felt like I was seeing the Dumbledore of the books again. So now I'm confused
Actually I think the character least like the book version is undoubtedly Barty Crouch Jr. but obviously they wanted the character a completely and utterly different way and this doesn't bother me. It was a shame they didn't do that sad scene when he's dragged away screaming by the Dementors, but I can see why they made him much more evil, particularly for the scene where he is discovered, as that felt a bit bland in the book.
And the Tonks thing? I'll defend Tonks and Natalia Tena till my dying day and I blame lack of allocated screentime for her problems. There was really no time to see Tonks' fun personality in OOTP and her depression in HBP was also cut, so very little of her character was seen which is a big shame.