From start to finish there are no wasted moments. All your emotions will be engaged. You'll laugh, you'll cry, you'll gasp in shock. What you won't be is bored. Don't plan on being able to take a bathroom break or get more soda and popcorn. You won't want to miss a second of this one.
There's plenty here for everybody: Good writing, humor, excellent acting, plot, action (that actually makes sense in terms of the plot), excellent cgi, eye candy. And it's a movie that needs the big screen for the full effect. Watch it in theater; don't just wait for the DVD.
If you saw Star Wars (the original) in the theater way back when, then this movie will evoke a similar feeling of awe. Once you see this movie, your perceptions of the movie-going experience will be changed. No other movie I've ever seen has hit me with the intensity of this one.