The reader, of course, is shocked by the diabolical efficiency of the murderer, and also by the fact that Montresor has lived with impunity, and also, ironically, his victim has rested in peace for fifty years.
Poe is using flashback to tell the entire story from 50 years after the tragedy has taken place. Montresor does not recognize this hand signal, though he claims that he is a Mason.
Is it worth going to jail over? Again, Poe makes the burial a long and drawn out process. Another fact is that Montresor seems very hospitable. With the imagery the writer uses for visualization of each setting and events such as; their trip through the vaults and catacombs in search of the Amontillado throughout the story, he creates suspense at different intervals.
It is also clear to the reader that Montresor is afraid while he is leading Fortunato along the cellar. In that era, it was generally okay for people to drink, more so than today. It may also be worth considering as to whether Montresor is a reliable narrator.
Likewise, Montresor's first words to him were "you are luckily met.