I really didn't find the movie Hunger Games to be vastly different than the book. There were a few minor changes and some small things left out, but other than that it matched up VERY well. In fact once I had it at home I went back and read a chapter-viewed a chapter-read a chapter, etc... and it matched up quite nicely.
I do see what cpltony is saying about letting yourself envision vs. letting the movie do it for you. And when I have read first in the past that has been the root of the problem in terms of my disappointment and nitpicking, because the film didn't look like *I* envisioned.
But what should be remembered is that just because *I* envisioned it a certain way doesn't make that way right or the way the film does it wrong. This is why I've been saying that from my experience it's been better to watch first and read second because you avoid that whole problem and are able to just take the director's vision as is. Then when you go back and read you *may* be stuck with that vision as you read.... but if you've got a healthy imagination (as I do) that can be replaced with your own vision as you read.