Breath of the Wild is an incredible game and a huge fresh feeling for the series, but there seems to be something missing from the game that would have, to me, made the game feel more complete.
I love shrines and hidden korok puzzles, but they're all pretty minor in terms of challenge and can start to feel tedious. There are fifteen regions in the game. Discounting The Great Plateau and the four regions containing Divine Beasts, we have ten regions that honestly feel pretty bare.
What if each area had one "main" dungeon – entirely optional just like everything else in the game, but at about the scale of the divine beasts? Where the Beasts provide story progression and assistance in the final battle, the regional dungeons could provide special items and upgrades to make the journey more challenging and exciting. These items could be permanent, or toggleable like the champion abilities.
Some ideas for dungeon rewards could be:
Titan Mitt/Power Bracelet: Pick up larger boxes/metal crates, throw weapons/rocks further, or harder to deal more damage. I honestly find myself rarely throwing weapons.
Zora Flippers: Even faster swimming. It's usually more worthwhile to glide over water or use Cryonis.
Hero's Bow: Unbreakable Bow, but not necessarily the strongest in the game. Maybe similar to the Twilight Bow in terms of arrow usage, or energy based like the Master Sword.
Upgraded Paraglider: Lower stamina use when gliding/increase gliding speed.
Bunny Hood: Run faster. I'm shocked this isn't in the game.
Pegasus Boots: Hold run without moving to charge, like Revali's Gale, and charge forward holding out whatever weapon you have.
Roc's Feather/Cape: Jump further/take less damage when jumping a distance.
Hookshot: There's just no excuse. Cross small gaps where trees/chests are around, stun enemies, grab items, get better positioning in enemy camps.
Grappling Hook: Hookshot can't grab rocky areas. Grappling hook could possibly be thrown to a high point on a mountain to speed up climbing, but not instantly draw you to it's contact point. Maybe pull stone/wood objects toward you, so you can fish things in the water magnesis can't grab, or pull rocks off of mountains from below if you're already in a fight.
Mirror Shield: Deflect energy based attacks, "breaks" like the Master Sword.
Bombchu: A Sheikah Slate upgrade for moving bombs.
Furthermore: Each dungeon could provide a stamina or heart upgrade. We never see Stamina Upgrades as rewards like we do Heart Containers.
For the items that are passive and toggleable, maybe make it so that only one or two could be used at a time, as to prevent it becoming too overpowered.
None of these items are required to complete the game, and would only serve to make your progression more enjoyable, or allow you more ways to approach situations. With the exception of the bow and hookshot, all of these items could be placed into the "key item" section and turned on/off like the champion abilities.
I love BOTW and it's new approach, but it just needs this extra kick.
Tl;Dr: Next game should re-add dungeons and special equipment to add more interesting ways to play the game, without removing the free-roaming style of gameplay.
Edit: formatting and added more items Edit 2: more items and clarification