It was marvelous. The stop-motion animation was gorgeous to a point that you often forgot they weren't CGI but actual dolls/puppets that's every movement was carefully orchestrated to make it appear seamless and real. If you haven't seen it yet, I certainly recommend it. That said..
The things they changed are pretty easy to see. Coraline's parents come across as harsher than in the book, the pace is faster and less creepy, the trips to the other house were more dreamlike and stretched out, there was the garden, there were several other small tweaks, and then there was Wybie. I'm not sure I like Wybie. While the character was likeable enough and I understand why the director felt the need to give a non-dead child character other than Coraline, he took more than he gave.
Yes, he introduced the doll which was a rather nice addition yet that could have been done without another character. While in the book Coraline is independent, smart, and rather clever this is diluted as Wybie helps her fill in gaps, to be brave, and to defeat the hand in the end. I honestly don't even understand the point of him, although I do admit there is a touch of sympathy as he's abused by the other mother.
Putting aside the bad, or at least iffy, addition, there was the garden. Fantastic. It was stunning and added a bit to the plot in helping the ghost children. The only 'eek' moment for me in the entire movie was when she was in the garden looking for the eyes and the other father springs to attack, lol. The praying mantis thing he rode was cool, along with all the other little gadget type things.
In all both the book and the movie had it's own set of charms while telling very much the same story. The director did the job of adapting the story in the book onto the screen in a way sure to entertain. I've seen it once and would love to see it again many times over. It's not perfect, though it's most definitely wonderful.