I have to disagree with El Bagu on this one, and say that toughen up the puzzles is a relevant part in increasing the difficulty in a Zelda games. Recent games have become easier because lack of threatening AI indeed, but puzzles aren't that difficult either. Sure, you can dump a whole lotta mosters while you are trying to do the puzzles, but that just makes the monsters the tough part. You should have a harder time solving the actual puzzles when it comes to puzzle solving rather than dying because of those gosh dern octoroks all the time.
A big part the lack of difficult puzzles is at the bosses often. Yes, it would've been harder if you needed to give them 30 stabs before they are defeated and they take away three hearts in a hit, but one of the most fun parts of deafeating the bosses should be figuring out how to damage them. I mean, look at Fyrus. A glowing gem in the forehead. Should I shoot him in the foot, durr durr? It's just a bit too obvious. Zelda 1 had a lot of puzzle solving in the bosses, but I think most of them were hard because of the limitations of the system. But it was still a great concept to explore the caverns and seek the old men to hear their advice to know how to hurt them. On the contrary, Zelda 3 wasn't much about finding the weak point in bosses, it was just a matter of knowing when to dodge and when to strike. I guess both ways of defeating bosses works great, let the player trying to find out the weak point and the hit it... for MASSIVE DAMAGE... or just completely ignoring that and make them alot tougher, but in any way should they be properly made and give the player a challenge.
Now lastly do I understand too how strange it would be to add a difficulty setting system for the puzzles in the games, becuase it would make the game very different depening on which setting you're on, almost too different. I am against adding it to a system like that, but pointing out that the system would then be kinda strange, since it only increases one factor of difficulty. So I guess my point is that I wouldn't mind a difficulty setting, I would enjoy playing the game with tougher enemies, but I don't want to see it as the sollution for the difficulty problem. It's not what I want to see in the next game so Nintendo can say "there, are you happy now?"
Because I wouldn't be.