I know that when movies are made based off books, the books are always better. And when I walked into the theater for Twilight I didn't have the highest expectations. I was still excited, but also worried.
And my overall opinion on it:
I liked it. Yes, it did have flaws, but it also had great moments too.
Some parts that were a little rough, and should have been edited better. And the movie definitely should have been a little longer and used a little more dialogue. In the beginning especially it felt like it skipped from when she first met Edward to months into the future with little transition. It was hard to see Bella and Edward's love fully and it felt like everything was rushed.

Overall, they stayed close to the events in the book and the order they happened in.
While I really wasn't sure about Kristen Stewart when she was first cast I think she did a good job as Bella(particularly in the scene where she was leaving Charlie), and Rob Patterson as Edward was ok. At some times he was a little awkward, but other times he seemed perfect as Edward. The best thing about Rob was his facial expressions. I know this sounds a bit weird, but they were hilarious!
The person that really surprised me though was the actor who played Charlie, Bella's father.
He was perfect, and had some really funny parts.
I loved the humor the minor characters bring into the movie (Mike and the window scene :D ).
My favorite quote would have to be from Edward though: "Sex. Money. Sex. Money. Cat"
The baseball and the ballet studio scenes were also amazing.