I'm not sure I would agree that no games other than those have gotten it right, I would wager you just haven't played other games ;)
Anyhow, check out this tech video about Unreal 4...this is likely to be the main lighting engine folks use for the next gen of games in the upcoming few years. IMO, this is lighting done right.
https://www.youtube.com/watch?v=MOvfn1p92_8
Its true I haven't played with a lot of games. But I am familiar with the techniques used. Contemporary games with moving shadows either colour tessellated vertices, or project a texture. Neither approach can capture what a shadow looks like. In this youtube presentation, though it didn't appear to be concerned with shadows, the shadows you can see are very Unrealistic. To begin with they are simply black or white, and there is no overlap going on.
You take a game like Dark Souls. Its just a basket of tricks to give your impressions of things like shadows. There are no particular light sources. And the shadows are just a texture projected straight down. So it doesn't flow over steps. It just seems to because the steps happen to not be level. Another way is to make textures from the point of view of each light. Textures appear pixellated and can't address more than a single plane. Vertices looks like saw teeth. I've never seen a game with volumetric vertex shadows, they tend to only be softened where each vertex blends into its nearest neighbor.
Ico's shadows are nice because they are vague, geometric, and placed by artists. Dark Slayer will just generate these kinds of shadows automatically, but in a more accurate way, so that you have all of the qualities of shadows. Umbra, penumbra, combination, falloff.
I mean if you are going to have shadows in a natural setting they should look like shadows above all else. But still shadows are really not important. In fact they are the last thing in the world to worry about. That's why photography is so much about shadows, because there isn't any else left to talk about. Its at the end of its rope.
PS: Dark Slayer's shadows will be baked in. If you want them to move they just have to be re-baked in real time. Probably moving shadows will be blended between frames so they can be recomputed every few frames instead of every single frame. Pre-animated shadows is an option. But I mention this only to say that the lights themselves can be modulated, flickered like fire light, turned on and off, etc, but they can't move without re-baking their shadow.
