Great Movie Ride was a big loss for me. It's a big part of what gave me my love of film (I've now seen about 12,000 movies overall, and own nearly 10,000). I made it a mission to see every film referenced on the ride and it took me years but I did it. Then they changed the ending video again so I had to find a few more. It and Backlot have given me a lot and it's a shame that I'll never experience them again. MGM was my favorite park for my entire childhood, and now it's a park that I don't even feel like I have to visit anymore (Although Star Wars will change that feeling at least).
Now if Tower of Terror, Space Mountain, or Dinosaur are ever seriously altered or removed, I'm not sure how I'll take it. They are why I love so many other things.