Ma-jor-as's Mask! :)
Personally, I think it is the best zelda game (yes, even topping Twilight Princess AND Ocarina Of Time.)
Firstly, the time system adding something new to the Zelda series. Another thing good about it was transformation. You could transform into a Goron, Deku, Zora and Omni Link. It really added versatility,
Also, IMO, it had the best side quest in existence, something which happened to involve two loves. I wont ruin it for others but lets say it involves you being a detective of sourts, and reuniting a couple ;)
The Main Storyline was good, especially the final boss'. Some were funny, and some were hard :(
The bosses were unique and strange (like having to unfreeze one...:\). Not only that some required upmost strategy to defeat :). Not only that, but you had to usually use the mask you recently got AND/OR the item. (With the exception of the first and last bosses respectively.) helping the tribes (Deku, Goron and Zora) also was quite nice. :)
Also, the characters returning from OOT under new 'identities' was either good or bad. personally, I loved it as I loved seeing familiar faces :)
Another thing is the storyline was really dark and mysterious, a change from most of the games at the time (much darker than OOT's IMO!)
Last but not least, the ending was epic! Not only did it have a suprise twist (if you played OOT anyway...;)) but it showed all of your achievements e.g: showing certain sidequests like the awesome one I mentioned earlier.;))
This post seemed more like a review than a opinion XD