What is a well developed character?

I keep hearing movie critics say that some movies don’t have well developed characters. What is a well developed character? Is it a character that you feel you know very well or is it a very realistic character? What makes Robert De Niro’s character in Meet The Parents less developed than his character in The Godfather II?

A well-developed character has some depth to him; his personality has facets that aren’t apparent just superficial, and he has some issues that have some real emotional resonance.

De Niro in Meet the Parents is just a collection of humorous traits, wheras his Don Corleone is motivated by much more serious factors. In general, dramatic characters are better developed than comic ones (one can’t say there was much depth in, say, Rufus T. Firefly), though there are exceptions.

Realism isn’t really the issue entirely (I don’t think Richard III in Shakespeare, for one example is particularly realistic, though he is very well developed). What matters is that the character gives the impression of a real human being, with complexities and contradictions behind what you see as a first impression.