This is pretty much the reason Steam says I've been playing a lot of Doom 3.
http://www.thedarkmod.com/The Dark Mod is a total conversion mod for Doom 3 inspired by the Looking Glass Studios stealth games Thief: The Dark Project and Thief 2: The Metal Age.
This is perhaps one of the best full conversion mods I've ever seen. If you liked the first two Thief games you owe it to yourself to play this mod, as it's probably the closest thing to a modern equivalent to the earlier Thief series there is. It builds upon the gameplay of those game while improving upon it in several ways and mimics their dark and moody setting.
The Dark Mod also has a very nice toolset for creating your own missions. Missions can be downloaded from their site or using the in-game downloader.
If you've never played a Thief game, then this is a stealth game set in a somewhat medieval gothic steampunk setting. You play as a theif, and as a thief you steal things (duh). Most missions involve attempting to acquire certain objects of great value as well as anything else valuable that you may find. Some missions may have more of a story involving other objectives as well.
The Dark Mod has it's own story and universe seperate from the Thief series. The wiki has information on technology, places, characters, and so on if you want to make missions that fit within The Dark Mod's setting.
A few of my favorite missions:
-The Knighton Manor
-The Beleaguered Fence
-The Heart of Lone Salvation
-St. Alban's Cathedral
It should be mentioned that this is essentially a mod made by hardcore Thief fans for hardcore Thief fans. Because of this it is often considerably more difficult than the original Thief games it is based on, so if you're not familiar with the gameplay you will probably be seen and killed a lot at first.
In the "downloads" section of the site they mention a few smaller and easier missions to start out with:
-The Crown of Penitence
-The Outpost
-The Parcel
-Too Late
I also recommend getting the "Sound Alert & Blackjack Trainer" mission to practice knocking out guards (which is more difficult than the original Thief games) and learn the sound of different floor materials.
Good things to know:
-One way to get some idea about what's on the other side of a door is to press your ear against it. Just lean against the door.
-Leaning forward (F by default) is very useful for getting at things at odd angles such as getting items from chests, pulling rope arrows out of wooden beams, and reaching out while hanging onto a ladder or rope. It can also help with spacing when using the blackjack or shortsword.
-You can open doors partially by using them again before they fully open, this is useful for peeking into rooms.
-If you're not sure whether a rope arrow can attach to a surface, shoot a broadhead first. If the broadhead sticks to the surface without breaking, then the rope arrow will too.
-If you want to mantle over an object without having to hold jump and risk accidently jumping, use press C by default.
-Blackjacking is much harder and more risky than in the original Thief games. You must hit the head and it does not work when guards are alerted and already have their weapon out. Also, helmeted guards can only be blackjacked from directly behind and you need to be much more accurate than with guards without helmets (I find it helps to aim for the base of the neck so the blackjack comes down on top of their head on its way down). "Elite Guards" who's helmets include masks cannot be knocked out with the blackjack at all.
-If you get caught and absolutely have to defend yourself, remember that armor does matter in this game. Trying to cut through a guard's helmet is not very effective. Generally you don't want to try to cut or stab directly at metal plate, go for weaker bits like chainmail, flesh, or cloth.
Some videos showing off a few of the mod's features:
Mantling/climbing
http://youtu.be/N0NQI__nsn0Object handling:
http://youtu.be/eR_0oW1VNSYCandles (also applies to most flames in general):
http://youtu.be/922ArtrKgC4A walkthrough of the mission "The Parcel" (somewhat outdated):
http://youtu.be/XrtlVpwTZsMEDIT:
A nice gameplay video of the mission "The Caduceus of St. Alban":
http://www.youtube.com/watch?v=d-fon8KWqn8&hd=1The wiki has more detailed info regarding controls, tools/gadgets, story/setting, and how to use the mission editor.
http://modetwo.net/darkmod/wiki/
