In one word: Pixar. Some of the other computer animated films have been alright (I enjoyed Shrek 1 and 2 when they were new, and more recently Cloudy with a Chance of Meatballs). Most of the other ones are not very good... I couldn't make it through more than half of Despicable Me.
Pixar has it all: they're original, funny, clever entertainment that everyone can appreciate and enjoy. Every movie utilizes computer animators who are the best at what they do and the constant advances in this relatively young filmmaking technology make every movie look better than the one before it. Like most, I found Cars and Cars 2 to be the exceptions to most of the above
I've been rediscovering these movies since getting my blu ray player and a high def TV. Computer animated movies are one of the best ways to show off your new digital entertainment set-up. I watched Legend of the Guardians in awe of the look of it without caring what was happening in the story for more than 2 minutes at a time.
Anyway, I could talk for a long time about why I like these movies, hope that gives you a bit of insight into the subject.
-Malone (28 yrs old)