What makes it so special is how it makes me feel. The landscape feels realistic, vast, serene, empty, wide open, a place to explore, not to check off to do list items. No quest marker or way point compass, simply hold your sword up and a beam of light will vaguely point in the right direction. The few things you do find on the way become special.
The isolation and sense of scale really comes into perspective when you happen onto one of the Colossi. Each one fits perfectly in its part of the landscape and is its own puzzle to figure out. The landscape and the Colossus are part of each other and soon you start feeling a sense of guilt for disturbing the peace for your own selfish gain.
Yet on to the next and so forth, until you wonder at the end if the end justified the means or if you've actually turned into the bad guy. Yet the rush of meeting each new Colossus is unlike any other boss encounter. The first time getting picked up high in the air, or under water, or found out in your little hiding spot underground, it's all unique and memorable.
SotC is a wonderful deviation from the usual, find something every 10 steps and have a dozen objectives going at once. It's not a min max game, it's not about loot or upgrades, it's just you wondering what you are doing literally and figuratively. No other open world game has this feeling. One quest, no distractions, no repeat boss fights. You actually can upgrade your most important ability, grip duration and also your health (less important). It's all you need, minimalistic game design for maximum effect.