Mate, I dont get it, I really do not.
A game is a very complex thing. It relies on many factors and things. Immersion is ONE of them for sure though.
Immersion comes from many things, be it storyline, gameplay, GRAPHICS, art style, physics, AI, effects etc.
Graphics can, have and are used to help gameplay. They DO help gameplay. So do effects, lightning and AI and physics.
Those need power. A lot of it.
You used to say that its theoretically possible to port STALKER to a PS2. Taking away the Dynamic Lightning, Weather effects, EAX, making worse textures and models, cut some shaders and other techniques and make maps smaller (by CUTTING CONTENT).
You will do it.
But thing is, you can NOT put the AI on the PS2. Even if the game looks 2.5D like DOOM by the time we are done with it, the PS2 simply can not handle the AI.
You will need to make a different game for it to work.
Sure the game may be good in its own right, make no mistake, but it will not be the SAME game but ported.
And to be fair, such an ugly, lifeless version of STALKER without all those tricks that help immersion ( a sellling point) and harm gameplay (lightning can illuminate the landcape during night, this is a gameplay element) will still just be too damn different.
The Crysis 1 that is on consoles is not THAT bad, it is playable and it has many of the features that make Crysis 1, well, Crysis 1.
But sometimes there are VAST differences in a game between versions. Crysis 1 simply cant play the same on a high level on consoles. The things that help immersion, the simplified AI (big change to gameplay) the worse effects that may aid gameplay result in a different game.
Its one thing to play a game with lower textures and models, lower framerate, longer loading times, lower resolution and wosre (but still the same) effects... its entirely different to play what is essentially a different game

In this case inferior unfortunately