The story would have been very different if told from Fortunato’s perspective. The main reason is that we have no idea what the motive for the murder is. This is always one of the main things you want to know. All we know is that there was some kind of vague and possibly imagined insult.
The thousand injuries of Fortunato I had borne as I best could, but when he ventured upon insult I vowed revenge. You, who so well know the nature of my soul, will not suppose, however, that gave utterance to a threat.
From this line we know that Montresor never threatened Fortunato, but we also know from the story that Fortunato never suspected he had done anything wrong. Why would he go into the catacombs with Montresor if he thought his friend was angry at him? If the story was told from Fortunato’s perspective, we may know what the injury was, or at least get confirmation that there wasn’t one.
Also, if the story was told from Fortunato’s perspective we would know what he was thinking. It really seems like he never suspected anything, until the last moment. It wasn’t until he was bricked in the wall that he realized he was being murdered.
"Ha! ha! ha! --he! he! he! --a very good joke, indeed --an excellent jest. We will have many a rich laugh about it at the palazzo --he! he! he! --over our wine --he! he! he!"
Since we only have Montresor’s perspective, it might be interesting to know what Fortunato was thinking during this time. At what point did he figure it out? Was he playing along? Was he just too drunk? This story will be told by either a drunken man or a madman. Either way, we will never get a straight answer on what went on.