"some" is an understatement. The changes it introduces completely trivialize the experience that was originally intended, along with the difficulty. The beginning of Stalker is supposed to be hard, you're supposed to struggle to find resources and weapons you get are mostly pea shooters. By doing it this way, progression is more satisfying. Complete mod makes weapons more accurate, makes sprinting infinite, significantly reduces weapon degradation (or completely removes it, not sure at this point), and increases inventory capacity to the point where all the aforementioned elements that make progression satisfying are neutered. Also, by making weapons more accurate, it neuters the enemy AI because the AI was designed around original limitations. They also reduced NPCs vision cones to make stealth viable, further trivializing the game. As far as I remember, it also added some sounds from Half-Life or other games that are completely out of place.