Also, are three any other landmark books that changed the way we comprehend history?
1) Within the field, because it was very well-written and, for its time, very well-done, based on exhaustive and honest consultation with primary sources available to Gibbon. He has biases, but he doesn't let them get much in the way of what his sources were telling him.
Generally speaking, because it was a highly intelligent attack on the effect of Christianity on Rome—Toynbee epitomized the work by the single quote: “I have described the triumph of Barbarism and Religion.” Given Europe's long fascination with that empire, such an argument punched culturally far above the normal weight class for heavily-footnoted, multi-volume tomes. (It was also written at almost the first time in history that such attacks wouldn't get its author executed or expelled from his upper-class society. It was a normal thing by then for British authors to assail "papism", but Gibbon had issues with the faith itself.)
2) I don't think Gibbon changed how we comprehend history—i.e. the nature of history or the process of constructing it. He just did a very good job of using his sources to try to change how we understood it—i.e. some of the conclusions and lessons to be found. As for people who changed how we comprehend history:
Using "we" as in Anglophones, eh, maybe Toynbee. He was almost Marxist in moving away from Great Man history to process and patterns. People did it before and people don't read him much now, but he did it in English and helped shift the narrative.
Using "we" as in European culture, the touchstones are Herodotus's anecodotal-but-well-researched History and Thucydides's more rational History of the Peloponnesian War. The Bible and Augustine's influential elaborations on it were major paradigms for most of the last two thousand years, viewing history as a specific narrative leading towards an inevitable conclusion. Hegel—and Marx and Spengler & al. after him—then tried to use philosophy and reason to argue for a similar narrative for human societies without a God above it or at its end.
Using "we" as in humanity, Sima Qian's anecdotal-but-well-researched Records of the Grand Historian essentially built historiography in East Asia.
In all these cases, though, it's not about history as an list of year-by-year events but rather as the construction of a meaningful narrative that explains why things happened in the past and offers guidance for the future.
3) As far as books that have changed that understanding... jeez, there are a bunch, but some that come to mind as important to the world you're living in now (that you see the effects of or hear people echoing arguments from, regardless of their actual accuracy) are
Gibbon is a fantastic writer, as informative as he is cheeky, and his works spanned a very detailed 1200 years.
He is well sourced, but he held a mean streak against Christianity as he was a product of the Enlightenment. That meant he had a strong and (I might admit) misguided bias and accused it (and organized religion in general) of being an agent for the Roman Empire's decline. He also ascribed to the idea of a Dark Age where "religion and barbarism" triumphed, which really isn't considered a fair representation of the Early Middle Ages. His writings on Islam aren't exactly trustworthy because of the limited information he had available, so his work isn't up to date on that subject.
For landmark historical literature I recommend The Histories by Herodotus and The History of the Peloponnesian War by Thucydides.