I agree. 2 years ago I got halfway through the book and lost interest in the series. A few days ago I saw the movie and now I'm finishing the book today (I just got to Chapter 27), and I have to say, the movie was pretty good except for all of the stuff that was skipped/altered/put in for no reason (Burrow battle, specifically. Wtf?) I was also a little disappointed when I saw what Slughorn looked like in the movie. I kinda pictured him like how he was described in the book. I like how Lavender Brown was portrayed though.
But alas, The Order of the Phoenix has always been my favorite book AND movie.