See, this is a difficult topic. Skyward Sword has shown that linear overworlds can turn away plenty of fans. It's not necessarily a bad thing, depending upon the game, but The Legend of Zelda is best nonlinear in my opinion. However, it's important that they make the best of the open world. Twilight Princess also set a precedent about too little in an open overworld.
I'll get this out of the way. Zelda U should certainly have an open world. However, it's more than just emulating Arkham City like you're suggesting. As a Batman fan, I'm well acquainted with that game's overworld. I felt like Arkham City, like Twilight Princess, had a bit of an empty overworld. I was expecting more fights with thugs, and I found a lot of altercations to be few and far between.
What I think would be a good overworld to emulate would be Assassin's Creed. Yes, I'm a huge Assassin's Creed fan, and it might be what's making me lean towards that, but when you look at Assassin's Creed's overworld, you find cities filled with city guards, all of whom may become hostile with a slightest crime. Zelda U should definitely strive for an overworld filled with enemies to fight.
However, in Assassin's Creed, they don't immediately engage you in combat; you either have to be notorious, or commit a crime. Therefore, it can have more enemies on-screen. Zelda, though, has enemies that attack on sight, so it would be important to not fill the overworld with too many enemies.
On the other hand, the overworld should be filled with hidden treasures that vary in rewards. More obvious treasures with small rupees, and the hidden ones deep in mini-caves containing Heart Pieces, or high-value rupees. It also wouldn't hurt to do what Twilight Princess did and have a few caves to explore. But there should be more than what we saw in Twilight Princess.
So yeah, an open world is ideal, but it must be done right. I'm sure Nintendo will do fine with the construction of Zelda U's overworld; they've done it plenty of times before.
I think a mix of both would be nice. With too open of an overworld you always risk too little in it, like Ganondork said. With a linear overworld you run the risk of boring your players. Perhaps the game could be cut into sections; one linear, one not?
I do believe an open-ER world would serve Zelda justice, not so much open world like Crackdown or Just Cause offer (maybe I'm saying no because their sizes are freaking amazing?), but tone it down just a bit and remove any traces of linearity in the game. LoZ wasn't linear except that you have to finish eight levels before you could enter the ninth..why should future Zelda break away from such an ideal?
Zelda games do have open worlds. They always have. It's... kinda their thing...
An open virtual world is one with very few boundaries or none at all. Open world environments allow for players to venture beyond a linear path through the game and engage in optional activities. Zelda has always been like this, although the degree to which Hyrule has been "open" is minimal as of late. For instance, Skyward Sword has very drawn in concentrated regions and the environments were designed to make players flow through branching pathways as we explored much like navigating the interior of a building. But as areas became available Link was free to explore them as he pleased and return to previously explored areas at will. The game did not close off previous regions and force us to explore a designated task.
Twilight Princess was very open but often made players wait to explore areas until the game was designed to open them. Heck, even paths between Hyrule field were arbitrarily locked until certain times. For instance, players could not access the Sacred Grove until it was time. A game that is more open would have provided access to the Grove even if there was nothing to do there along the main quest line. But the same is true for many open world games. In Arkham City, for instance, Penguins Museum isn't accessible until Batman finds the code to disable the security. That takes place at a pre-determined point in the game.
So, to me, Zelda games are open world... but out of everything in the series I strongly believe they can certainly be much more open then they have been. For instance, I would prefer to be able to attempt dungeons in any order.
I'd love for the Zelda games to expand upon their overworld, not just removing the linearity where we are forced to complete dungeons in a set pattern but to also add more side quests that have nothing to do in the main quests. This would mean that I can complete the first dungeon of the game then explore the overworld and secret dungeons/caverns, acquire different items & weapons from these dungeons, hopefully even level/gear Link up a bit so he's much stronger and afterwards I could choose to continue my main quest.
I think that the main quest dungeons shouldn't be the places to collect items that you'll later need for side quests, it should be that I collect items I'll need for side quests while doing... side quests. Meaning I could gear my character up with a lot of better items, weapons etc. then decide to tackle the main quest. This would be a truly open world to me, I'd have more control over what I want to do and how I want to play the game.
If I want to collect all heart pieces in the game before tackling the second main dungeon of the game I should be able to do so, if I want to get the best sword in the game after I find my first sword I should be able to do so without getting stopped by plot / dungeon barriers.
The reason I didn't like the original Zelda is because it lacked linearity and was solely based on exploration. I think this wasn't very good because you are left with no idea what to do and most likely you would be sitting there like a lemon, wondering what to do. Of course that is the whole point of exploration, but it wouldn't hurt to include slight hints on where to go.
Obviously this was just the starting point of the series but over time the games became more linear, which in my opinion was an improvement. I think Ocarina of Time is the strongest game when it comes to balance between exploration and linearity because there are some Dungeons/Temples that you can do in any order which didn't require a certain item or Storyline to progress e.g You could complete the Water Temple before the Fire Temple since the Megaton Hammer isn't required to complete the Water Temple.
I think linearity is important in Zelda and it shouldn't be removed completely. What Nintendo should do is recommend which Temple to go to first, but you can decide yourself afterwards where you will go. by doing that you have some linearity but you also have the feeling of an open world where you can explore to your hearts content, much like A Link to the Past. I'd rather enjoy myself and have some idea what I'm doing instead of exploring around in circles wondering "what I'm I supposed to do?".
I haven't played Batman: Arkham City so I can't really compare. All I can say is that an open world can be incredibly tedious - or - make the game incredible.
Seeing as dungeons are found when new items are found, meaning you know what item to use and where (normal zelda formula), if an open world meant you could go to a dungeon without knowing you needed to obtain an item, you weren't forced to obtain, to get through puzzles, this could really change the game for bad or for worse, dependant on the skill level of players, or just opinions. It's a tricky one.
I think what he's trying to say is without some form of linearity, it will be very difficult to progress the game and eventually you would stop playing it due to boredom, this is exactly how I feel when I play The Legend of Zelda. If you compare it to recent Zelda games, then in I do see where DarkestLink is coming from.
Many ways in general, but in the case of a "too open world", there's the issue of lack of direction and weaker sidequests that don't make use of the games items. Technically speaking, this does not have to be the case, but if you keep sidequests that do make use of the items, you make little use of the open world itself.
It's best to keep the world slightly restricted until a point of the game where you have the resources to make use of an open world.