Which CD-i Zelda? The one where you've got to bomb some Dodongos, the one where you rip out that heart "Good!", or the one with the cosplayer and the Renaissance festival rejects?
I know that the series has moved quite a distance away from the openendedness that the early games thrived upon.
Actually, dungeon order's been pretty linear for all of the games after LttP. They're still open ended in that you can kind of piss off and explore the world at your own leisure -- which was true for the 3D games I played, after an initial, more linear portion that was maybe about 1/4 of the game -- but the dungeon order was either fairly rigid or you could sequence break but it wasn't really intended or optimal. And generally, zelda sidequests are always exploring for heart increases, or getting upgrades to you equipment. Which, again, never changed.
That's true, but I think what I was getting at was the perceived value of the pickup diminishing over time.
In the Original you had a total of 16 hearts and outside of random heart drops or the occasional fairy only up to two doses of potion to bring that back during a dungeon run. Meanwhile you eventually started facing down stuff like Darknuts and Wizrobes that could take a full heart per hit with the Blue Ring on and you could wind up getting swarmed due to bad luck or an untimely tag from a Bubble left you swordless. In this game each heart is worth a lot (especially since you can't upgrade your main weapon until you have either 5 or 12 heart containers depending on the sword). ALttP is quite a bit easier than 'enemy turned into you or started spamming magic, you're probably going to eat a hit now' and more generous with its health upgrades but at the same token things generally hit harder and especially once you hit the Dark World and now everything's taking off at least a full heart if not 2 or 3 per hit suddenly 10 hearts is a lot more valuable than 6 or 7 hearts. Granted you had bottles and fairies (but they weren't full heals) in this game but until you got the mail upgrades near the end you basically had to rely on the volume of your total health as your measure of defensive growth.
Whereas you have the 3D games where suddenly, outside of the occasional outlier like Iron Knuckles, nothing hit you for more than a full heart and with 20 hearts and bottles that can hold free full heal fairies (and for the N64 games a half-damage upgrade) suddenly all those pieces of heart don't seem to matter all that much after your first or second container to get you out of your starting 3 hearts faster. Enemies and challenges don't scale well at all for most of these games and only recently with games like TP and SS have enemies even tried to keep up while nerfing the power of potions and fairies.
Likewise where and how you've assembled your inventory has changed over the years as well. In the Original you had to find or buy a sizable portion of your inventory outside of dungeons (Blue Ring, Magical Shield, Power Bracelet, Letter, Blue Candle, Wooden Arrows, Bombs, White and Magical Swords, and Potions), and dungeons themselves sometimes had more than one item (First Quest had Levels 1, 5, 7, 8, & 9 and Second Quest had Levels 4, 8, & 9). In ALttP where they toned down dungeon items to one per dungeon there were still quite a number of optional items to be found outside of dungeons (like the Bombos Medallion, the Bug-Catching Net, the Magic Boomerang, the Red Shield, the Tempered and Golden Swords, the Magic Cape, the Cane of Bryna, the Mushroom and the Magic Powder, Bombs and their and Arrow expansions, a Magic Meter expansion, and Bottles). OoT was still pretty good about optional items as well (with the Ice Arrows, two of the three Spells and two of the other three fairy upgrades, Deku Nuts and their and Seed and Stick expansions, Bomb Bag and Arrow Quiver expansions too, Beans, the Golden Scale, the Hylian Shield, the Giant's Knife and Biggoron's Sword, the Wallet expansions and the Stone of Agony, three of the Bottles, the Tunics, the Mask of Truth and other assorted masks, Epona, her song, the Sun Song, and the Cow I guess).
Around MM is where optional items start to phase out in favor of heart pieces and rupees due to the pre dungeon item needed to enter the dungeon (leaving the wallet, bomb bag, and arrow quiver expansions, Bombchus, Deku Nuts, five out of six bottles, all but the first Great Fairy upgrades, the Razor and Gilded Swords, the Bombers' Notebook, the Song of Soaring, and 18 out of 24 masks or 17 out of 24 masks and the Bomb Bag) although the masks were a fair tradeoff at this point. WW on the other hand lets you ignore (the Tingle Tuner, the Picto Box and its upgrade, the wallet, bomb, arrow, and magic meter expansions, the upgraded spin attack, the Hero's Charm, the Magic Armor, three of the bottles, and perhaps the Song of Passing, the Bait Bag, and that utterly broken Elixir Soup, plus 51 out of 60 charts and that stupid Nintendo Gallery).
The tl;dr of this :goonsay: post is that I just feel like exploration in Zelda games have been offering diminishing returns over time.