To me it is almost flawless and for whatever reason still stands the test of time graphically. It still looks good, whereas a lot of n64/ps1 games look horrible now.
I remember I was at a friends house and saw his older brother playing the water temple, visually I had never seen anything that incredible or large in scope...I only had a sega genesis (and an NES) at the time. Imagine 2D sonic the hedgehog with its 2 minute long levels compared to a giant action/adventure 3d RPG game.
The 3 dungeons as a kid are great, all the adult dungeons are great. All are just perfectly designed with excellent fun boss fights at the end. A lot of the replay value is in the dungeons. The dynamic of the world being different in the past and future, seeing how the locations and people have changed. The sidequests are excellent, from important stuff like getting the horse, or finding the ghost of Dampe.... to other activities like horseback archery. Its kind of nuts... to really go through all of the excellence in this game would take a while...the music really fit all the locations perfectly, the size and scope of Hyrule Field, the cleverly placed secrets, the excellent puzzles....etc etc...Whats sad is that most Zelda games after this tried to follow a similar formula but they never could get the same feel, never could reach the same mastery ever again. And also even playing it now there really isnt much anybody could say that could be added or tweaked to make the game better. 20 years of gaming innovation and you cant touch that game.
I need to get my n64 and run through it again.
edit- the kids of today will never know about fishing for the Hylian Loach