First off, I will say (as I usually do) that the book was better! No big surprise there. However, the movie was very well done. Some elements of the book were left out, obviously due to time constraints, but overall it did not bother me so much. I guess because the actors that were chosen for the main roles were great choices. I thought Eric Bana as Henry was a very good fit. He is a good actor and has been overlooked in the past, but I think this movie showed off his dramatic chops. Rachel McAdams, of course, was ethereal. I just think she lights up any role she plays. She has a very bright future in acting. And Ron Livingston as Gomez...outstanding! It was just regretful that his part in the movie was so much less than in the book.
Now there was one thing I missed in the movie and that was the comic relief. As I said in my review of the book, what was great about it was the combination of science fiction, tragedy and comedy. The movie was mostly focused on the two latter elements. There just wasn't enough comic moments to balance the sad ones. However, I was glad that the movie eliminated the constant lovemaking between Henry and Clare. I'm not a prude by any means, but I think the movie portrayed well the great love between the two without having to show constant sex, like the book.
So, in conclusion, I do recommend that you see this movie, but if you're a reader or if you were planning on reading the book, I would suggest that you read the book first. Reading the book first really keeps the confusion at bay and fills in any holes that might have your mind full of question marks. And if you really must choose between the book or the movie...choose the book.