This play certainly challenges the reader's preconceived notions about drama and how plays traditionally work. Generally, readers assume that the play will have several characters who will face at least one significant conflict; there will be some significant setting and probably multiple sets/settings; there will be some action; the characters will do things; the resolution of the play will provide satisfaction to the reader at the end of the conflict(s).
This play barely addresses ANY of the above features. There are only two characters, Vladimir and Estragon, for the majority of the play and only two other characters, Pozzo and Lucky, drift in and out of the scene having absolutely NO effect on the main characters. The setting is incredibly sparse -- a tree and a rock -- and it only ever changes in that the tree seem to grow leaves overnight between Act 1 and Act 2. The characters don't ever do anything but talk and attempt to alleviate their ill-fitting hat and boot. Their sole purpose is to wait for a man(?) named Godot to come and tell them what to do.
The meaning of the play comes from the existential state of the two men. They are not taking control of their lives -- they are condemned to be free. Instead of doing anything to understand, or even better, change their situation, they merely wait around for Godot to come. Estragon can barely even remember that they are waiting. They talk about leaving, about killing themselves, about their dreams and nightmares, their want of better food, their memories of the previous day and the characters of Pozzo and Lucky, but they do nothing. Nothing comes of anything. They are existentially dead. By Beckett's stripping away all of the expectations and leaving only the most absolute essentials of a story, he leaves the audience with a stark picture of these two men and the tragically unending circumstances of their lives. The ending provides no resolution, just as their lives have no resolution.