You talking about behind the scenes as in AI? Any engine can handle that, its just the devs have to program it into their game. And any engine can be dark, its just again how the devs program it. Cryengine is obviously made for Crysis games so the demos and pics will be based off that bright island type atmosphere. Change the lighting type and vuala you got what you want. I think the perfect example is the UT3 engine. Its in many different types of games but when you think UT engine you think UT.
Well - not so much AI as compared to X-Ray's "A-Life." Most games, AI is only the coding and behavioural characteriscs for NPC/AI within a certain distance of the player. Generally, with almost all games, this is limited to the current map the player is on, and AI is down to combat behaviour. Usually, there's a set number of AI active at any given moment, and these are usually down to scripted AI, or force-spawned AI.
The A-Life system is ten-fold more complicated than that. STALKER handles up to thousands of AI at any given moment, spanning across all the game maps. They're delegated to either "online" or "offline" status - in "online," they're within a set distance of the player, and full behavioural characteristics are determined . . . their friendliness towards the player, where they are, what they're doing, where they're going, etc. The player can interact with them, i.e. talking, trading, fighting, etc. It's a bit more fleshed out than standard FPS AI in this mode. In "offline" mode, they're outside of the player's immediate radius . . . but the engine continues with various aspects. If the AI is going to point A on map X, they slowly go there over time. If they cross enemies will en route, the engine simulates the fight, and determines winner/loser, etc. Inventories are still active, and NPCs can and will trade with each other. They'll hang around certain points for random periods of time, before moving on to other areas. They'll find food, sleep, explore, search for goods/equipment, loot enemies and stashes . . . They'll also go out and attack other locations . . . and all this is handled "behind the scenes," unless the player moves within distance that they're turned "online," in which case, the player can then come back into contact with the AI . . . as well, the vast majority of the AI isn't scripted, per se, but spawned randomly. Spawn points are typically set, but the engine randomly determines NPCs names, equipment, faction, status, and other errata based on numerous preconditions and factors.
Granted, the vanilla version of the game had disabled a lot of this, or it wasn't yet implimented - but modders have re-enabled these features, or continued to push the boundaries of just how many AI the engine will accomodate, and what they're capable of doing . . . even going so far as to keep track of AI reputation and experience standing, and also use those factors for determining interaction.
TBH, it handles all of this much like a simulation game would . . . it's just that it's behaviour that is not common of the FPS. Sure, I have no doubt other engines could handle such work . . . but as it stands, almost all other game engines were never designed with this kind of complex AI in mind from the start.
) and CS.