According to a large number of people, Final Fantasy 7 is one of the best video games of all time. While some may disagree, there are a multitude of reasons why this is so.
At the time (1997) Final Fantasy 7 was one of the first normal looking 3d games of its time. To make matters even better for the game, it was truly massive, a whopping 1GB (which was substantial at the time). At the time the average computer hard drive size was around 5-10 gigabytes.
Final Fantasy 7 also caught on because it was one of the most well put together Final Fantasy games of its time, if you exclude the quality of the graphics. There were seamless transitions between cut scenes and normal game play to where players never had to see a black screen followed by sudden, completely different graphics.
Also there were several really fun mini-games that were the best the Final Fantasy worlds have ever seen. The most famed one was Chocobo racing/breeding which was one the best side game of any Final Fantasy to date.
It's for these reasons and more that Final Fantasy 7 was one of the best games of all time. It's a vague summary but if you want details on any one of these points feel free to search the internet for it. The game's been around so long, it's easy to find information about anything Final Fantasy 7 related.