It's rather intriguing to think that a game can be Not Hard and still be Fun. Legend of Zelda: The Wind Waker is definitely Not Hard. I just beat the game last Friday night, besting Ganondorf (and his Puppet sub-boss) on the first attempt. Sure, I had three Fairies-Suffocating-In-Bottles and a life meter about 16 hearts long... but still, I stumbled into two major boss sequences, sussed out the weak spots and general strategy, and layeth the smackdown without much trouble.
I suspect that Wind Waker purposely geared down the difficulty for two reasons. #1) Accessibility. Nothing is more frustrating than having a game you love but end up being simply unable to win. From Nintendo's standpoint, the game has so much extra stuff to do that it's quite all right if the main quest errs on the side of easy. #2) Presentation. Normally, when you die during a boss fight, you have to rewind time and enter the boss fight again... breaking the illusion of living a video game character's real-time challenge. But if the boss fights aren't too terribly hard, and you win on the first time through, you maintain the pace of the game's storyline. No duplicated scenes, you see.
And the Ganon fight certainly has a great deal of storyline attached to it. It does cheapen the whole experience if you have to keep restarting and skipping cutscenes. The game's other bosses - Kalle Demos, Jalhalla, etc - aren't as big a deal, storyline-wise... so they can afford to offer a tougher gameplay fight.
Great ending, by the way.
But about the Fun. In Wind Waker, the real meat of the game is exploration and sidequests. You can spend hours and hours sailing the seas, taking Picto Box pictures, unscrambling slide puzzles, tracking down secret treasure chests, and uncovering hidden dungeons. In that respect, the game is very similar to Grand Theft Auto, in that the game creates an ongoing, changeable world in which you are free to roam at your leisure. And even if combat isn't especially difficult in most situations, it's always a blast to play and to watch.
What we're seeing is the new face of quality in adventure video games: multiple simultaneous goals, interactive and evolving environments, and a built-in ability to scale according to the user's level of commitment. GTA, Wind Waker, Pokemon Sapphire, MGS2 - and any given low-level RPG, really - all work this way to one level or another.
I suppose it's really just the modern iteration of adding replay value. Pack in a bunch of junk that you can do during or after the "main game." Pizza delivery missions, collecting photographs, pokemon beauty contests, toying with sentries. I think it's great, because I hate getting locked into one linear path... especially when it starts to suck and you'd like to take a break (Wolverine's Revenge, I'm looking at you right now.)
The only feature I'd like to see in the next Zelda game would be a friggin' quest checklist. Wind Waker almost figured this out by letting you find specialized maps that reveal locations of Fairies, Octos, Heart Containers, etc. But the maps won't tell you which ones you've found/completed and which ones you have left to find... which just pisses me off, frankly. My memory just isn't good enough to keep track of every little sidequest, so give me a little help here, Nintendo. TRIPLE the quests for the next Zelda game, but include a way to organize them all! Link needs a PDA.