Shock 1 was extremely interactive and simulational. Yet they are probably two of the most immersive products I've every played. Half Life gets its immersive value from unmatched in engine presentation of story elements and Shock gets them from letting YOU make a lot of the story, by giving you so many ways to express yourself as a character in the game in the form of the myriad gizmos, gadgets, ways to approach a problem, etc. Half Life is an extremely well stage managed experience. The developers generally knew how a player would approach a problem, evinced by the nearly entirely linear game design.
Shock is extremely open ended and exploratory.
We give you a world and some guidelines, but what you do within that world is up to you. These are key elements in the Shock immersive experience. Shock 2 takes the RPG aspect of Shock step further by giving you a choice in how you develop your character internally. Our job is easier from a presentational viewpoint and much much harder from a game balance flow issue. Weapons can break, be repaired, be modified, etc.