I'd give it a solid 8.
For the longest time I could not get into MM, no matter how hard I tried to like it. I tried it again this earlier this year and something about it made me fall in love with the game. The entire Ikana segement was one of, if not THE most most fun I had playing a Zelda game.
I'd talk about the story but anyone who has ever even read a post on here reguarding MM will already know how strange/deep it was. It was a game that fleshed out NPCs'.
That being said, I do have some complaints. The final Boss was WAY too easy. I remember when
OoT first came out, one of the main complaints was that Ganondorf was way too easy,so I cannot even begin to imagine how fans took Majora when donning the Fierce Deity Mask. All you really have to to is Z-target and press B numerous times, then you're done.
Another complaint is how absurd it was to find some of the masks. For instance, what wold possibly posess someone to bust out the Lens of Truth near Ikana to find a lone, invisible soldier? maybe I missed something, but it gave absolutely NO hint anywhere in the game about Jiro. This really only goes for a couple of masks, but I had to vent it out.
I know it seems like I'm not too big on MM if you read the last couple paragraphs, but I really enjoyed the game as a whole, and still think it's one of my top 5 games for the N64.