The first two I viewed were Watership Down and Plague Dogs. I enjoyed Plague Dogs more than Watership Down, but both were entertaining, even though very depressing at times. For older films, the animation is superb. It takes a lot of hard work to put in so much detail in making an animated animal look real that other companies don't want to put the time and money into it. So, they make the cartoony versions you see in films such as Madagascar. If you're going to check these out, let me give you a warning. Even though these movies were meant for children...that is not the case. There are many gory scenes in Watership Down which I kind of like because it takes away the whole cutesy title of rabbits and shows that like all other animals, they shed blood to survive and protect their territories. Plague Dogs is much the same.
Here's an amv someone made with most of the disturbing scenes of Watership Down to a Marilyn Manson song (why would you do that bro)