I think it's just a great game that has completely stood the test of time; it's not really nostalgia for me because I only played it for the first time around two and a half years ago, and I'd agree that it is one of the best games of all time. The graphics are very solid much easier to go back to than say, FF7. The soundtrack is just magical; music often really makes the game for me (of course that's why we're all here isn't it?)
Although as someone who played OoT and TP in around the same time frame, I think it probably is nostalgia making so many people say that OoT feels more massive than TP. I mean seriously, TP is just epic and the soundtrack is pretty great too.