The city is populated by three sects. There's the Order of the Hammer, or the Hammerites. They're a dogmatic, theocratic religious group who follow the works of the Builder, their deity. And as is so often the case for those who approach life as a hammer, they see everything as nails, including Garrett. The Pagans, almost unmentioned in this first game of the Thief series, but absolutely integral to the plot, are a primitive, almost animalistic group. Equally unexplained are the Keepers, the secret society who trained Garrett, and aren't as ready to let him go as he is them. Their involvement is gentle and refined. (Both groups are explored in much greater detail in the following two Thief games.) How much you learn about them really depends on how much effort you put in.
Take notice of the details, read the quotes from various texts during the beautiful cut-scenes, make sure to pick up all notes and parchments you find, and listen in to the conversations of others you sneak up on, and you can start to piece together an intricate and involved world that's been meticulously conceived and realised. This graceful design would go on to be bettered by Deus Ex two years later, but Thief's delivery will always be the subtler.
It's the size that counts
Oh, come on, how can I love anything more than the epic scale of the game? It's enormous. Even the first few missions are vast, sprawling events, surprising you with twists and turns, events changing your previous goals, tunnels taking you on huge diversions. You're negotiating ancient trap-filled catacombs, or fleeing bizarre dinosaur-like beasts in rugged caves, or taking out perimeter guards of opulent mansions, for hours and hours before the game's central story even begins.
Games just aren't half this big any more. One mission just before the midway point gives you a few simple tasks, breaking into the Downwind Thieves' Guild to steal some valuables from Lord Randall. It seems like an elementary couple of buildings to pick your way through. It's anything but. The buildings are the iceberg's tip, concealing the miles of caverns, underground living quarters for the thieves, and enormously complex sewage system, that winds its way under the city. Stealing a sapphire vase has never been so involved. And this is all without such nonsenses as load points - just acres of uninterrupted content.
By the time the key themes of Viktoria's tasks, the Eye, and the elaborate triple-crossing conspiracy come into play, you're so expert with your lockpicks, so adept at traversing hazardous environments with your water, moss and rope arrows, and so capable of blending into shadows, that you feel you deserve the title of a master thief.
I fear I trivialise the game with my silly gimmick. But as I play it, I can't help but have those thoughts of competing love. Its ability to make me feel affection toward carpet may sound trivial, but it's emblematic of its overall achievements. It's so complete, so engrossing, so terrifying. And it's so adaptable. If you love killing everyone in a room, play on Normal and go for it. If you love entering and exiting a building without changing a single thing but for the volume of wealth left behind, then go ahead and leave every soul untouched. Or if you're me and you love knocking them out by sneaking up right behind them, or luring them into your trap with a distracting noise, then piling them up in a dark corner, then play that way.
Looking Glass's reputation has become legend, but it's going back to games like Thief that reminds you how it's more than deserved. Thief is an embarrassment to modern stealth games, each of which produces only a faded parody of this masterful original. It makes me sad for a lost era of truly epic, truly intelligent, truly brilliant gaming. Many games manage one or two of these, but so few achieve all three. However, being sad is ridiculous when you can go back and play this masterpiece again. There's so much to adore.
Addendum: The Thieves' Codec
To adore it, however, now requires a few tweaks. I strongly recommend getting hold of Thief: Gold, not only because it has three extra missions that elaborate on the main story, but also because it fixes many bugs and improves textures throughout.
However, if you want it to work on your XP or Vista machine, you're going to need to do a few tweaks. There are no more helpful pages than this one on the Eidos forums and this one at TTLG, which solve the most frequent issues.
But let me tell you right now you'll want to install the VP7 codec and definitely, definitely follow the instructions on the previous links to ensure Thief is only running on one processor if you've a dual/quad-core machine - it will definitely crash without either of these. Also, if you're using an NVIDIA graphics card, then I strongly recommend getting the NVIDIA Driver 5x.xx Fix from Thief-TheCircle.com. It will prevent the horrible texture memory usage bug that will make the game pretty unplayable otherwise - but be warned, you'll have to have the original disc in the drive when you play if you do this.