Let's clear something out of the way right now : Igor is an animation movie, but mainly not for children. Kids will not understand most of the jokes as the topic for most of them are intended for an older audience. There is, however, a visual comedy that will apply to younger viewers, but overall I think this movie targeted teenagers and adults.
People will like Igor based on what they expect from the movie. If they expect it to be like Wall-E and other Pixar movies, you probably will be disappointed. Igor has it's good sides and bad sides. The visual side was breathtaking, the setting is beautiful, with unorthodox character design. However in some cases, like the king of malaria, it seemed like a copy of Nightmare Before Christmas' mayor, and that was disappointing. The story is not too bad, but not the best. It lacked a bit of depth at some times, but it is still amusing and entertaining.
Overall Igor is a good animation movie. It's not the best, definitely not the worst. It's definitely worth seeing for animation fans, people who like Tim Burton's work (as the design in the movie is similar to his style), and anyone who wants to enjoy a light story with a happy ending.