Movies are an attempt at escapism - if you view them as a means of getting away from real life for an hour or so (or in some cases - three hours) and emersing yourself in a different world, then you may be satisfied with the movie, if you view them to go and find fault and pick holes in the story/technology/actors, then of course you will walk away possibly dissatisfied.
In saying that, I was very disappointed with Happy Feet, from the trailers it appeared to be a movie aimed at kids about a penguin that could not sing but could dance - not a movie that turned into a political rant about the environment.