ICO's merits allow it to stand tall as one of the few games whose essence truly will endure historical wear and tear.
The premise of ICO and the primary motivation for moving onward are simplistically one and the same. Having both been trapped in a castle for their own respective reasons, the titular character and his companion, a girl by the name of Yorda, must find a way to escape and go out into the world. That alone may not necessarily sound thoroughly original, but the game's minimalistic style of storytelling allow it to still nevertheless feel unique. What it lacks in depth is made up for in spades in immersion, as the player is given the chance to weave their own sub-tale of sorts as they become more and more attached to Yorda.
The literal version of that attachment is actually one of the two defining aspects of ICO's gameplay. As one traverses through the castle, they are often holding hands with the girl in an effort to stay together. This is especially a necessity during times of combat, in which the castle's shadowy minions obsess over retrieving Yorda and preventing her escape from coming to fruition. Moments when she is forcefully separated from the player are incredibly tense ones, as everyone's livelihoods ultimately rest on her survival. Even when there is not any actual fighting to be done, though, moments when there is not direct contact with Yorda are still anxiety-inducing, as being away from her has its own shares of implications, even when it is needed in order to proceed forward. A bond is formed between Ico/the player and Yorda to such an extent that it is difficult not to care about her. This is despite the fact that it is impossible to verbally communicate with Yorda because she does not speak the same language as the protagonist, further emphasizing the need to be together as often as possible.
The other defining facet of ICO's gameplay is its almost complete reliance on environmental puzzles. While certain mainstays such as the movable block are present, many others are more natural to the game's setting and as such require that creativity be used during the solving process. It all looks as though it is part of a castle, first and foremost, and while few puzzles require a lot of thought, none of it is overly blatant, either. From the purposes and abilities of each acquirable weapon to what can be used as climbing surfaces, the player must often derive the underlying context of why something is there in order to get past the current obstacle and proceed to the next one. Thankfully, the process is consistently smooth with little backtracking whatsoever, making ICO a fairly linear game despite initial appearances.
What really helps set ICO vastly apart from virtually every other game in the action-adventure genre is its attention to detail in a number of oft-overlooked areas. Yorda is where a lot of this can be found and, if she's given enough mind, can be the source of minute awe-inspiring moments that are not directly related to the gameplay. If left to her own devices, for example, she may go off on her own and look at the scenery or watch some bird fluttering about in the current area. Or, if the player inadvertently hits a wall with their sword or stick, she might yelp in fright. She always manages to consistently show depth in areas where other tag-alongs in video games have been historically lacking. It is these and other such nuances in the game that ensure that the game's minor things stand out just as well as its major ones. They add plenty of spice to a flavor which is already highly exotic.
Graphically, ICO emphasizes its environments and animations over everything else. The former, while having clearly aged since the game's 2001 release, still hold up very well stylistically. They do not necessarily push the PlayStation 2 to its breaking point, but they are still well-crafted and deserve plenty of applause for ensuring that nothing ever looks monotonous despite the singular nature of the setting. ICO's animations are a very nice extension of its devotion to detail, as they often capture even more little things which could easily be missed without a close inspection. From the hesitant delicacy which Yorda clearly has before clearing major jumps to the manner in which clothing is toyed around by the wind, the animations in the game are very well crafted. Other parts of the game's visuals such as character models do not have quite such lofty standards, but nevertheless manage to be stylish in order to make up for that fact. The frame rate also stays steady for the majority of the gameplay, with only slight falters in very few instances.
ICO's sound design can only be accurately described as very deliberate. The majority of the playing time is spent without music, leaving the ambiance up to the environments. When it actually is present, it is always very low-key, being well-composed without overstepping its bounds and breaking into something overly (and unnecessarily) symphonic. Despite its seemingly obvious absence, the music is not something which is missed over the course of the gameplay, as those previously-mentioned ambient sounds succeed at immersing the player in the game's world. The game also employs a small amount of voice acting. Fictional languages are used for the verbal portion and they too do not go above and beyond their limits, which works perfectly fine. Corresponding subtitles are issued, although it should be noted that Yorda's are not in any earthly language whatsoever.
The scope of ICO's achievements are profound. Few games before it have been able to abide by a minimalistic design mentality and actually have that work to their benefit. But because it always knows exactly what it wants to do in every conceivable area, ICO's vision shines through very vividly and because of that fact, its merits allow it to stand tall as one of the few games whose essence truly will endure historical wear and tear. It is not only a testament to the legacy which the PlayStation 2 is bound to leave behind, but also a testament to the unique characteristics which only video games can wield. Consider it a must-play for anybody interested in how flexible the medium can be and how that affects its profoundness in myriad ways.