Ico is a work of art. Atmospheric, lonely, mysterious - as much about the Castle as Ico or the Princess, its historic!
At base, Ico is mostly a journey wrapped up in a puzzle game. While you will need to do a fair amount fighting true, the fighting is clearly secondary and much more of a means of the Castle's expression as you seek to lead the captured Princess out of the darkness and into the light.
As a puzzle game, it is challenging - each section of the castle providing the sort of obstacle that will require a lot of trial and error, thought, and probably plenty of looking online to figure out how to proceed when stuck, as you will be stuck frequently. However, if you persevere through the puzzles and keep at them, you'll find the solutions always work out, and that often what you mistook for environmental design was in fact an interactive part of the game. As a game involving combat, you'll find that while you're not often challenged to a high degree of fighting skill, (Ico isn't a fighter really) you will need to save often so that when things do go array, you're not re-tracing your steps as much as you may be otherwise. More likely than dying in a fight, or having the Princess sucked into oblivion, you'll jump of a cliff when you're not paying close attention.
But let us come again to my main point - Ico is more work of art and journey than fighting or puzzle solving, and from the opening sequence which is full of forboding mystery, you'll understand that this isn't your typical Zelda remake.
Right away, you'll notice something incredibly unique - there is no music to speak of, only the ambient noise of the howling wind, crackling fires, and cavernous but empty rooms. It is at this point that you'll realize that what you're actually interacting with is the Castle itself - a boss with numerous traps, tortuous and grand in vision with few equals. The sound design only heightens your awareness of your solitude on your journey, of the flickering incandescence of the princess which you seek to save, and as you encounter massive hall after grand vista, all hallowed in their secret darkness, you will find that more than any other game, Ico presents an aesthetic of atmospheric loneliness without contemporary comparison.
The sound isn't the only thing that'll make the Castle come alive, however. The artistic rendering of the waterfalls, birds, grand vistas - all will fulfill their purpose. And the dark queen who rules the mystical place, radiating a wickedly black electrical aura, will stun you with her presence such that you'll feel that she IS the Castle which she rules, and the dark minions which she sends out after you will soak into your mind as the ravens of Poe.
But the ambient sounds and artistic vistas will be compounded by the interaction of Ico and the princess. This interaction's focal point, of all things, is in the simple yet elegent grasp of hands between the two. While it would've been all to easy for this interaction to be forced, it is rather stunning in that when holding hands, they visibly link and their bodies will stop each other, pull each other, and jerk in a quick movement. In fact, given the number of times that you'll need to catch the princess as she leaps over a chasm to you, its amazing that each and every time my breath catches, as the physical representation is such that it always feels as if the princess is going to slip away forever. Such is the representation which draws you in in such a manner as you make you believe in what you see - a rare feat indeed.
Just about every aspect of this game has the sort of touch of a master's craft and all the love that goes into a staggering vision where each aspect of the game is there to serve the single-minded vision of a lonely and haunting place where your only companion is a ghostly girl and the majestic search for a way into the world of substance and light, as if emerging from Plato's cave of appearances into the real. Such a craft is timeless in that when the graphics are long dated, the puzzles worn, and the castle walls themselves in danger of crumbling down into the dust of forgottenness, such a wonder as Ico will remain as a ghostly reminder of what a game could be. Simple put, it's a masterpiece.
oh, and make sure to watch all the way through the credits... fyi