What is the relationship between the father and son in The Metamorphosis?
While Gregor's father has certainly seemed to exploit him, using his son to pay off his own debts while he lounges around the house eating leisurely breakfasts and taking naps, there is also some evidence that he was once in nearly as pitiable a situation as Gregor. We learn in Chapter 2 that Gregor's father had not worked for the past five years, and that these years "were the first vacation of his hard-working yet unsuccessful life." In other words, then, despite the fact that Gregor's father worked so hard, never taking time off, he never achieved any measure of success. This is not the way it should be, should it? There should be some correlation between hard work and success, shouldn't there? And yet, this older man has worked and worked and only has a "business disaster"—the one in which he accumulated the debt that Gregor now pays off—to show for it.
Similarly, Gregor works and works, and yet on the first day ever that he has not shown up on time, his manager actually comes to his house to talk about what a terrible job he does! The manager badmouths him to his own family! Therefore, we can assume that Gregor, despite his very hard work and total lack of a social life, cannot be considered successful now either. Perhaps the experiences of father and son, then, are not so different. Both seem to have at least one thing in common: they both know what it is like to work and work and never be appreciated for it, never achieve anything like success as a result of it. It seems, in many ways, to be an indictment of capitalism and what it does to workers like them (those who do not own the means of production). Both Gregor and his father have been victims of this system, though neither seems to possess an awareness of this fact.
The relationship between the father and the son is strange. It is certainly strained, but it is also complex. The son's metamorphosis begins while works in a job that he hates in order to pay down his family's debt. His father loves him, but his love seems difficult to find: although tears eventually come, his initial response to his son's transformation is not sadness, but anger (he shakes his fist). The twisted part about their relationship is that the son essentially gets sick while carrying his father's burden (debt) but the father, instead of being sympathetic, essentially rejects and attacks the son for becoming the "vermin" that he has become. He hurts his son, physically, and scars him (he throws apples at him which injure his son and eventually cause an infection). This is deeply ironic, because the change in the son seems to occur as a result of the work that he does on his father's behalf. The father should be showering him with love, but instead hates the despicable creature he has become and wants nothing to do with him.
The father and the son have a strained relationship. This is one reason why Gregor "morphs" into a huge bug and stays in his room.
Gregor is expected to work and support the family who basically does nothing until after Gregor's metamorphosis. Then, suddenly, everyone--including the father--is able to stand up and pull his or her own weight in the family since Gregor is no longer able to do so. Gregor's breakdown is bad for him, but good for the rest of the family.
Check out the excellent summary and critical analysis on enotes for this story.
Just to add food for thought - the relationship between father and son in the book is meant to be reflective of Kafka's relathionship with his real father. Kafka had stated at one point that he felt like an insect in his father's presence. His father was large and imposing in appearance while Kafka was small and weak.