I am also one of the guys who likes all modern Zelda games.
And I personally won't understand the items as keys thing. You need the raft to get to Dungeon 4 in Zelda 1. You need the ladder to complete dungeons 5 and 7. You need the arrow to defeat Gohma and the Ocarina to defeat Digdogger. And Zelda 2 is also like that. You can't see anything in the caves, get the lamp first! You can't reach the platform, you need a higher jump! In every Zelda, the items act like keys. The difference is to find out which "key" you have to use in that situation.
And exploration? Zelda 1 clearly offers the most exploration, even though just the first three dungeons are explorable in any order from the beginning. But the other Zeldas are quite good when it comes to exploration.
Majoras Mask had tons of secrets, I think it has even more than any other Zelda game.
Wind Waker had 49 isles and you only visit like 20 of them for the story. T
wilight Princess had 4 big caves and finding these caves actually were one of my most favorite parts of this game. And still, there are many areas you can only reach through items in Hyrule Field, like the top of Hylia Bridge.
Skyward Sword, unfortunately, subverted it somewhat. The areas are more complex than in all previous 3D games, yet there is barely anything to find that wasn't story-related. The sky would've been great if there would've been several treasures already "unlocked". Still, you don't have to go to most of the bigger isles and I know that there are several areas in Skyward Sword, especially the volcano I haven't explored on my first playthough. Still, it feels like there is less exploration than in the previous ones. But it is there.
Btw: Is there a Workshop for the next Zelda? I want to see what everyone wants to see in the new Zelda. I already had a case where someone complained that he wants innovation in new Zeldas, and when Skyward Sword came out he suddenly complained that it was too different and the previous Zeldas had enough innovation.