Another Screwed up Book to Movie

I just went to see "Percy Jackson and The Olympians: The Lightning Thief". Now before I go on, I'm am going to say a few things. First, I have read the book, thought it was awesome, and was really looking forward to seeing this movie. Second, I thought the movie was pretty good. The reason I had a problem with it was because I've read the book, and from the start, the movie starts messing with the plot of the book. I don't want to give examples and spoil anything, but there were characters completely missing, changed up plot points, monsters missing, completely new items; I could try listing every changed point I saw, but I give away spoilers for those who haven't read the book and for those that haven't seen the movie. Plus, it would just take too long. Now I know I said it was a good movie, and I stand by that. My problem is, the movie could have been better. There were better story surprises, twists and turns, and a completely different ending in the book, and most of it wouldn't really be that hard to do. If you've read the book, here's a fun thing to do. See the movie, and then try to list as many differences between the two as you can. Geeze, and I thought the movie version of "A Series of Unfortunate Events" messed with the book plot.