One of the other things I always liked about Thief is that there's surprisingly little separation between the story and the gameplay. In a lot of games, especially FPS-style games, the first-person HUD gets in the way of elaborate cutscenes. It's a very limited way to frame a scene, and while that's good for play, it's bad, or at least inconvenient, for art. Traditionally, plot is seen as an interruption to action gameplay and is confined to specifically-defined chunks of story, usually stuck between levels as a way to get the player from one place to the next.

Thief does use third-person cinematics between maps, but there's at least an equal chunk of the plot contained within the play space. The pace of gameplay is fluid, often slow, and huge amounts of exposition are given via documents and other media Garrett finds in the places he's bent on robbing. By pausing before you wonk people over the head, you can overhear conversations that range from important and helpful for your housebreaking, to random and hilarious. Particularly in the second game. Your tutorial mission involves rescuing an indentured servant girl your buddy's in love with, so they can get married and he'll shuddup about it. If you eavesdrop in the right place later on, you can hear the girl's former mistress howling at one of the city guards, delivering an entirely inaccurate account of what went on to a very bored desk sergeant who is not at all interested in taking down a report.

Their sound design is also phenomenal. After you get through The Metal Age, crackly phonograph cylinders will give you the creeps for the rest of time.

One of the most interesting parts of this lack of separation, however, is  that it also affects the borderline between story conventions and the story itself. Garrett is sharp almost to the point of being genre-savvy; only the conceit that what you're hearing is his internal monologue keeps him from actually breaking the fourth wall with a lot of his snark. He's unnervingly good at knowing exactly how he is going to be shafted, by whom, and when -- his commentary is sophisticated and occasionally rather prescient, though presented as if it stems from experience and cynicism. The times when he's taken by surprise by twists are also when the player is similarly caught.

It's hinted that this is actually an in-universe ability of his. His back story, as presented quite early on in the first game, is that as a small sticky-fingered urchin out on the streets, he was able to see a Keeper, a sort of word-based magician from an organization so secret and unseen that their entire HQ building is totally mystically invisible to the inhabitants of the City. Not only was the Keeper not hidden from him, he was unaware that the man was supposed to be hidden, to the point where he thought it was a great idea to try and pickpocket the guy. Didn't work, but it impressed the hell out of the Keeper.

The one glaring exception to this is at the end of the first game, when for some reason he is not skittish about hiring on with someone extremely slippery to steal a giant magic gemstone. And this, too, is hinted to have reasons behind it. It makes some sense when he embarks on the mission, as the other people involved in the plot have annoyed him, and Garrett displays a distinct tendency to steal and break things out of spite when someone pisses him off enough. He doesn't like being herded into a corner and shoved into doing things, and Constantine is doing less shoving than everyone else.

But it's rather strange how unruffled Garrett is when the Eye starts hissing at him telepathically in the middle of the heist. Having been with the Keepers for a while, he's not unaccustomed to magic thingamabobs, but none of the other ones ever tried to talk to him. Even the player can see Victoria's betrayal coming a mile away, but he seems taken completely by surprise. He resents the hell out of the Keepers for having to swoop in and save him, but strangely seems to carry no animosity towards the Eye, either as the object that prompted, or a sentient thing that demanded, Victoria's decision to take one of his own personal eyeballs, the excruciatingly hard way. Garrett snarks about having to steal the Hammerites' frigging Chalice yet again at the end of the the third game, but has no real objection to having to come back into contact with the creepy gemstone.

It's never explained explicitly, but the cyclical nature of the City is made clear at the end of Deadly Shadows, and the Eye is rather fixated on the connection it has with Garrett. The implication, I think, is that either the Eye was using a pre-existing link to Garrett to draw him into closer contact, until they could exchange points of view (the Eye 'stole' Garrett's eye, and claims to use it to see; Garrett, in exchange, ends up with a mechanical replacement eye, built by the Hammerites, that lets him zoom and do other things that are not-quite-human), or that their meeting was so strongly predestined that even Garrett couldn't manage to fight it.

There's also the way the antagonists in all three games turn out to be almost one-dimensional. Also intentional, as the ending makes clear. The City precesses around the three axes of its magic until its course becomes so eccentric that it hits the extreme ends -- one antagonist is dedicated to chaos, one to crushingly extreme order, and one to total self-centered greed. At which point, someone shows up to tell them all off for being completely insane. Not a bug, but a feature. I tip my hat to the writers for that.