I would never really call it overrated because of just how good it was back then. Now, I personally have not found the enjoyment in it as other people have (A Link to the Past is, and always will be my favorite), maybe because I never beat it, or maybe because I found it was lacking. I see no reason why it shouldn't be as highly praised as it is; I'm guessing people are going to praise Skyward Sword just as highly down the road - at least in my opinion. I understand that it's been a huge deal and everyone understands how good it is, but you have to understand not everyone has played the game just yet. I've owned the game for three years and I'm only at the Spirit Temple, imagine where others might be.
As far as the overall hype goes, it's because the game has gotten such high ratings that it's unbelievable. I don't think I've ever seen a game get rated higher. To achieve such a rank, the amount of praise that it still received is well-deserved. For long-time Zelda fans it might be annoying - I've only been a Zelda fan for six years, and I'm tired of hearing its constant hype - but that doesn't make it annoying for newcomers. You have to keep in mind that there are still new fans coming in (I started Zelda with Twilight Princess and decided to buy every Zelda there is) that might want to give the game a try. This hype could be very beneficial to these people since they'll know it's worth paying for.
Overall Ocarina of Time is a great game. I don't think it's overrated, only because it earned all of this praise through great gameplay, good graphics (in its time) and an amazing story.