I must say, I was pretty gosh darn impressed. In the books, Tris has a very subtle (or not so subtle) character transition. She's still the Adnegation girl she was raised to be, but as the book progressed and she became stronger, she began to change. Tris didn't turn into some stone cold GI Jane or anything but she develops a tougher exterior but she still has the same heart. I wasn't sure if Shailene Woodley would be able to pull of the character changes but she did a pretty good job. I was very engaged and I didn't look at her as that irritating pregnant chick from ABC Family. As far as I'm concerned, that's the most important part of a book to movie adaptation.
Things in the movie will change, parts will be left out, and we, as readers and watchers, have to accept that and shut up. Many of the authors that I follow on Twitter of Facebook (John Green, Kim Harrison, and more) constantly say that when their books become movies, they don't mind that the characters don't look exactly as they've described, or if things are changed, what matters is that these actors can fully portray the characters that the authors have created. I wouldn't have minded a slightly tougher Christina, but other than that I have no complaints. It was a great movie.