Thanks for the comments.
Another really interesting system for character AI is Goal Oriented Action Planning (GOAP). This was used in F.E.A.R. and is similar to the way Sims interact with objects in their homes. Basically, each NPC or enemy has a set of goals that they want to meet (like killing the player). Each object in a level contains information on which goals they are connected with (ammo, weapons) and the AI runs through a grid of options similar to pathfinding nodes to see which goals they must meet first in order to accomplish their major ones (before you can kill the player, you need a gun and if it's not loaded, you need to get some ammo and load it first). Stalker has something similar to this too, but a lot of it is stored in "smart terrains" instead of individual NPCs and objects.