It's hard to say why Meet the Robinsons was so under rated as a Disney movie, potentially poo marketing as the same year it came out so did Ratatouille, Pirates of the Caribbean: At World's End, National Treasure: Book of Secrets (the real loser), High School Musical plus so more mostly direct to video movies. It was a big year for the number of Disney movies that were released.
The movie itself was fantastic and I think a lot of people didn't appreciated it as deeply as it was created. It's probably one of the most watched movies in my household.