I'm gonna be one of those people that says yes, indeed it is. On my list of greatest games, it's tied with Final Fantasy VII. Even after playing through both games numerous times quite religiously, paying attention to minute (and large) details, I honestly can not choose between the two games. Yes, it is a tie. Here is my reasoning (warning: this will be quite lengthy)...
Gameplay: Gameplay for both games was fantastic. In OoT, Nintendo did a more than perfect job of transitioning from a 2D world to a 3D world. Same credit goes to Squaresoft in Final Fantasy VII. OoT made perfect use of the Z-targeting system and your item usage. FFVII had an excellent leveling system and magic (materia) system that was incredibly customizable and encouraged you to innovate. After careful review, both games score high in terms of gameplay
Story: I can't exactly nitpick with the story in a Legend of Zelda game, but nonetheless the story was quite engaging and I really did feel an emotional connection between the characters. Final Fantasy VII scores better in story imo, as the story had a very complex plot, with numerous subplots and extremely deep characters who each had their own trials and tribulations throughout the game. Because of the uniqueness and depth of the story in FFVII, that game gets the edge over story and plot. But like I said, when it comes to Zelda games I don't try to emphasize plot and even with that in mind you can still argue a great case with Ocarina of Time, even up to a story giant like Final Fantasy VII.
Gameworld: Both gameworlds were very fun. As I said earlier, both games made a more than perfect transition into 3D.Part of what made this transition so perfect was the fact that the worlds were so detailed. In Ocarina of Time, the world was indeed fun to navigate through (Gerudo Valley, Lake Hylia, and Kakariko/Death Mountain area come to mind), and the dungeons are very very memorable. In FFVII, the world is enormous with many locations you can travel to, with something to do in each location. If I were grading this on size and depth, FFVII would get the edge in terms of the gameworld, but since I'm rating it based on how well the world fits into the game and it's relationship with other aspects of the game, both games score even.
I could go on about other things that the games set standards in (like the fantastic soundtracks to both games, etc.) but I'm just gonna stop here before I become WAAAY too lengthy. In summary, Ocarina of Time is absolutely the greatest game of all time, but my position is that Final Fantasy VII is also so incredible that it basically ties up with Ocarina of Time in terms of greatness.
This isn't a decision I made lightly, either. I didn't just sit down one day and call it a tie in order to stop thinking about it...it resulted in a tie because I thought about every aspect of the game carefully after doing numerous runs in both games. Now I'm going to stop before I bore all of you to death.