Overall, I think "The Open Window" is a very good story. I have read it many times over the years.
Here are some thoughts that have occurred to me recently in connection with the construction of the story:
Framton Nuttel is represented as a nervous wreck, a man on the verge of a nervous breakdown, a neurotic and a hypochondriac. This aspect of his character is so apparent that it is possible to overlook the fact that he is a terrible bore and a nuisance. Vera never says a word about how boring she finds the man, but her aunt speaks for both of them when she tells her husband:
"A most extraordinary man, a Mr. Nuttel," said Mrs. Sappleton, "could only talk about his illnesses, and dashed off without a word of good-bye or apology when you arrived. One would think he had seen a ghost."
Framton is there on a very slender pretext in the first place. He has sent a letter of introduction from his sister--but his sister was there four years ago, and these people hardly knew her. Now they are stuck with a stranger they have felt obliged to invite to tea. And it looks as if he is hinting that he wouldnd't mind being invited to stay for dinner. He tells Mrs. Sappleton about his doctors' advice in some detail and concludes with:
"On the matter of diet they are not so much in agreement," he continued.
This seems like saying, "You don't have to make any special cooking arrangements if you want to invite me to stay for dinner."
Vera is not just having fun with Framton. She dislikes him. He is not the least bit entertaining or attractive. She would like to make him leave and not have to put up with his hanging around for tea and then perhaps for dinner. So she makes up a clever story to frighten him into fleeing.
It seems unusual that the three hunters would return through an open French window. They have been mucking around all day and are covered with mud. The spaniel too must be wet and muddy. And they are carrying some dead birds in their hunting bags. Saki wanted them to appear heading for the open window so that Framton would be properly frightened. So he made a big point of describing the open window and even titled his story "The Open Window." Mrs. Sappleton tells Framton:
"I hope you don't mind the open window . . .. my husband and brothers will be home directly from shooting, and they always come in this way. They've been out for snipe in the marshes to-day, so they'll make a fine mess over my poor carpets."
Why don't they come into the house by a side-door, take off their muddy boots, makes sure their guns are unloaded and put them away, leave their dead snipe in the kitchen, and then enter the living room properly? Why would Mrs. Sappleton tolerate three men tramping all over her carpets in muddy boots after "they've been out for snipe in the marshes to-day"? In the marshes!
Saki must have hoped his readers would overlook this incongruity because he wanted to make everything happen in a single setting which would be easy for anyone to visualize. He provided the liviing-room with floor-to-ceiling French windows so that the three hunters would be clearly visible to Framton from where he was sitting. Not only that, but he specified that one of the windows was left wide-open when it was getting dark outside and must have been getting cold in England in the month of October, when the story takes place.