Indeed, classifying Beckett's work with definitive terms is a challenge. There are moments in the work where comedy does present itself, and there are equally challenging moments where pessimism reigns supreme. In its articulation of the human condition, the play exposes that much of the human condition lies in between different polarities. It is fairly impossible to draw one such judgment in a setting, but rather explore how the predicament of human beings might constitute different experiences at different moments. There is a certain level of pessimism that is revealed at the ending when Godot defers his arrival for another evening. While Beckett is making an existential statement on the human condition, one cannot deny that the notion of waiting and the paralysis that results is an integral part of the human predicament. In this light, pessimism is an understandable experience on the part of the reader/ viewer.
In short,"Waiting for Godot" is neither comic nor pessemistic. It is absurd. Estragon and Vladimir wait and wait and wait for Godot. But what amounts to their waiting? Nothing. This play is a classic of "Theatre of the Absurd". It's philosophy is bleak regarding the human condition. In addition, the style of writing that depicts that vision shows humans acting in a meaningless world, trying to make meaning. This theatre is based upon the philosophy of existentialism. For example Sisyphis, in mythology rolled the bolder up the hill forever. He had no choice regarding his life; he was doomed to do it forever.(his fate) However, he did have the choice over how he interpreted it. Other writers like Albert Camus and Jean-Paul Sartre were similar to Beckett in depecting an impersonal universe.
Waiting for Godot is a subtle exploitation if not subversion of the genre of comedy. It is a 'tragi-comedy' as Beckett called it or a 'tragical farce' as Ionesco would call his play The Chairs. Beckett's play kills off both tragedy and comedy because it redefines both the discourses with a radical edge to the redefinitions. The play is a kind of a black comedy and whether it is pessimistic or optimistic is a question made redundant by the double bind created by the playwright. It is this kind of a binarization that the play denies. It is pessimistic in the announcement that Godot will not come but the stoic resignation in the insistence on the waiting act in itself spells hope and courage. Beckett's work is all about encountering the disaster where going on is almost impossible and it is precisely in such horrendous difficulty that the Beckettian man gets going with the WILL to go on and the drive of compulsion.